Publications by year
In Press
Chadburn SE, Burke EJ, Gallego-Sala AV, Smith ND, Bret-Harte MS, Charman DJ, Drewer J, Edgar CW, Euskirchen ES, Fortuniak K, et al (In Press). A new approach to simulate peat accumulation, degradation and stability in a global land surface scheme (JULES vn5.8_accumulate_soil).
Abstract:
A new approach to simulate peat accumulation, degradation and stability in a global land surface scheme (JULES vn5.8_accumulate_soil)
Abstract. Peatlands have often been neglected in Earth System Models (ESMs). Where they are included, they are usually represented via a separate, prescribed grid cell fraction that is given the physical characteristics of a peat (highly organic) soil. However, in reality soils vary on a spectrum between purely mineral soil (no organic material), and purely organic soil, typically with an organic layer of variable thickness overlying mineral soil below. They are also dynamic, with organic layer thickness and its properties changing over time. Neither the spectrum of soil types nor their dynamic nature can be captured by current ESMs. Here we present a new version of an ESM land surface scheme (Joint UK Land Environment Simulator, JULES) where soil organic matter accumulation - and thus peatland formation, degradation and stability – is integrated in the vertically-resolved soil carbon scheme. We also introduce the capacity to track soil carbon age as a function of depth in JULES, and compare this to measured peat age-depth profiles. This scheme simulates dynamic feedbacks between the soil organic material and its thermal and hydraulic characteristics. We show that draining the peatlands can lead to significant carbon loss along with soil compaction and changes in peat properties. However, negative feedbacks can lead to the potential for peatlands to rewet themselves following drainage. These ecohydrological feedbacks can also lead to peatlands maintaining themselves in climates where peat formation would not otherwise initiate in the model, i.e. displaying some degree of resilience. The new model produces similar results to the original model for mineral soils, and realistic profiles of soil organic carbon for peatlands. In particular the best performing configurations had root mean squared error (RMSE) in carbon density for peat sites of 7.7–16.7 kgC m−3 depending on climate zone, when compared against typical peat profiles based on 216 sites from a global dataset of peat cores. This error is considerably smaller than the soil carbon itself (around 30–60 kgC m−3) and reduced by 35–80 % compared with standard JULES. The RMSE at mineral soil sites is also smaller in JULES-Peat than JULES itself (reduced by ~30–50 %). Thus JULES-Peat can be used as a complete scheme that simulates both organic and mineral soils. It does not require any additional input data and introduces minimal additional variables to the model. This provides a new approach for improving the simulation of organic and peatland soils, and associated carbon-cycle feedbacks in ESMs, which other land surface models could follow.
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Abstract.
2023
Piilo SR, Väliranta MM, Amesbury MJ, Aquino-López MA, Charman DJ, Gallego-Sala A, Garneau M, Koroleva N, Kärppä M, Laine AM, et al (2023). Consistent centennial-scale change in European sub-Arctic peatland vegetation toward Sphagnum dominance-Implications for carbon sink capacity.
Glob Chang Biol,
29(6), 1530-1544.
Abstract:
Consistent centennial-scale change in European sub-Arctic peatland vegetation toward Sphagnum dominance-Implications for carbon sink capacity.
Climate warming is leading to permafrost thaw in northern peatlands, and current predictions suggest that thawing will drive greater surface wetness and an increase in methane emissions. Hydrology largely drives peatland vegetation composition, which is a key element in peatland functioning and thus in carbon dynamics. These processes are expected to change. Peatland carbon accumulation is determined by the balance between plant production and peat decomposition. But both processes are expected to accelerate in northern peatlands due to warming, leading to uncertainty in future peatland carbon budgets. Here, we compile a dataset of vegetation changes and apparent carbon accumulation data reconstructed from 33 peat cores collected from 16 sub-arctic peatlands in Fennoscandia and European Russia. The data cover the past two millennia that has undergone prominent changes in climate and a notable increase in annual temperatures toward present times. We show a pattern where European sub-Arctic peatland microhabitats have undergone a habitat change where currently drier habitats dominated by Sphagnum mosses replaced wetter sedge-dominated vegetation and these new habitats have remained relatively stable over the recent decades. Our results suggest an alternative future pathway where sub-arctic peatlands may at least partly sustain dry vegetation and enhance the carbon sink capacity of northern peatlands.
Abstract.
Author URL.
2022
Chadburn SE, Burke EJ, Gallego-Sala AV, Smith ND, Bret-Harte MS, Charman DJ, Drewer J, Edgar CW, Euskirchen ES, Fortuniak K, et al (2022). A new approach to simulate peat accumulation, degradation and stability in a global land surface scheme (JULES vn5.8_accumulate_soil) for northern and temperate peatlands.
Geoscientific Model Development,
15(4), 1633-1657.
Abstract:
A new approach to simulate peat accumulation, degradation and stability in a global land surface scheme (JULES vn5.8_accumulate_soil) for northern and temperate peatlands
Abstract. Peatlands have often been neglected in Earth system models (ESMs). Where they are included, they are usually represented via a separate, prescribed grid cell fraction that is given the physical characteristics of a peat (highly organic) soil. However, in reality soils vary on a spectrum between purely mineral soil (no organic material) and purely organic soil, typically with an organic layer of variable thickness overlying mineral soil below. They are also dynamic, with organic layer thickness and its properties changing over time. Neither the spectrum of soil types nor their dynamic nature can be captured by current ESMs. Here we present a new version of an ESM land surface scheme (Joint UK Land Environment Simulator, JULES) where soil organic matter accumulation – and thus peatland formation, degradation and stability – is integrated in the vertically resolved soil carbon scheme. We also introduce the capacity to track soil carbon age as a function of depth in JULES and compare this to measured peat age–depth profiles. The new scheme is tested and evaluated at northern and temperate sites. This scheme simulates dynamic feedbacks between the soil organic material and its thermal and hydraulic characteristics. We show that draining the peatlands can lead to significant carbon loss, soil compaction and changes in peat properties. However, negative feedbacks can lead to the potential for peatlands to rewet themselves following drainage. These ecohydrological feedbacks can also lead to peatlands maintaining themselves in climates where peat formation would not otherwise initiate in the model, i.e. displaying some degree of resilience. The new model produces similar results to the original model for mineral soils and realistic profiles of soil organic carbon for peatlands. We evaluate the model against typical peat profiles based on 216 northern and temperate sites from a global dataset of peat cores. The root-mean-squared error (RMSE) in the soil carbon profile is reduced by 35 %–80 % in the best-performing JULES-Peat simulations compared with the standard JULES configuration. The RMSE in these JULES-Peat simulations is 7.7–16.7 kg C m−3 depending on climate zone, which is considerably smaller than the soil carbon itself (around 30–60 kg C m−3). The RMSE at mineral soil sites is also reduced in JULES-Peat compared with the original JULES configuration (reduced by ∼ 30 %–50 %). Thus, JULES-Peat can be used as a complete scheme that simulates both organic and mineral soils. It does not require any additional input data and introduces minimal additional variables to the model. This provides a new approach for improving the simulation of organic and peatland soils and associated carbon-cycle feedbacks in ESMs.
Abstract.
Qiu C, Ciais P, Zhu D, Guenet B, Chang J, Chaudhary N, Kleinen T, Li XY, Müller J, Xi Y, et al (2022). A strong mitigation scenario maintains climate neutrality of northern peatlands.
One Earth,
5(1), 86-97.
Abstract:
A strong mitigation scenario maintains climate neutrality of northern peatlands
Northern peatlands store 300–600 Pg C, of which approximately half are underlain by permafrost. Climate warming and, in some regions, soil drying from enhanced evaporation are progressively threatening this large carbon stock. Here, we assess future CO2 and CH4 fluxes from northern peatlands using five land surface models that explicitly include representation of peatland processes. Under Representative Concentration Pathways (RCP) 2.6, northern peatlands are projected to remain a net sink of CO2 and climate neutral for the next three centuries. A shift to a net CO2 source and a substantial increase in CH4 emissions are projected under RCP8.5, which could exacerbate global warming by 0.21°C (range, 0.09–0.49°C) by the year 2300. The true warming impact of peatlands might be higher owing to processes not simulated by the models and direct anthropogenic disturbance. Our study highlights the importance of understanding how future warming might trigger high carbon losses from northern peatlands.
Abstract.
Verbeke BA, Lamit LJ, Lilleskov EA, Hodgkins SB, Basiliko N, Kane ES, Andersen R, Artz RRE, Benavides JC, Benscoter BW, et al (2022). Latitude, Elevation, and Mean Annual Temperature Predict Peat Organic Matter Chemistry at a Global Scale. Global Biogeochemical Cycles, 36(2).
Crichton KA, Anderson K, Charman DJ, Gallego-Sala A (2022). Seasonal climate drivers of peak NDVI in a series of Arctic peatlands.
Sci Total Environ,
838(Pt 3).
Abstract:
Seasonal climate drivers of peak NDVI in a series of Arctic peatlands.
Changes in plant cover and productivity are important in driving Arctic soil carbon dynamics and sequestration, especially in peatlands. Warming trends in the Arctic are known to have resulted in changes in plant productivity, extent and community composition, but more data are still needed to improve understanding of the complex controls and processes involved. Here we assess plant productivity response to climate variability between 1985 and 2020 by comparing peak growing season NDVI (Normalised Difference Vegetation Index data from Landsat 5 and 7), to seasonal-average weather data (temperature, precipitation and snow-melt timing) in nine locations containing peatlands in high- and low-Arctic regions in Europe and Canada. We find that spring (correlation 0.36 for peat dominant and 0.39 for mosaic; MLR coefficient 0.20 for peat, 0.29 for mosaic), summer (0.47, 0.42; 0.18, 0.17) and preceding-autumn (0.35, 0.25; 0.33, 0.27) temperature are linked to peak growing season NDVI at our sites between 1985 and 2020, whilst spring snow melt timing (0.42, 0.45; 0.25, 0.32) is also important, and growing season water availability is likely site-specific. According to regression trees, a warm preceding autumn (September-October-November) is more important than a warm summer (June-July-August) in predicting the highest peak season productivity in the peat-dominated areas. Mechanisms linked to soil processes may explain the importance of previous-Autumn conditions on productivity. We further find that peak productivity increases in these Arctic peatlands are comparable to those in the surrounding non-peatland-dominant vegetation. Increased productivity in and around Arctic peatlands suggests a potential to increased soil carbon sequestration with future warming, but further work is needed to test whether this is evident in observations of recent peat accumulation and extent.
Abstract.
Author URL.
Mackay H, Plunkett G, Jensen BJL, Aubry TJ, Corona C, Kim WM, Toohey M, Sigl M, Stoffel M, Anchukaitis KJ, et al (2022). The 852/3CE Mount Churchill eruption: examining the potential climatic and societal impacts and the timing of the Medieval Climate Anomaly in the North Atlantic region.
CLIMATE OF THE PAST,
18(6), 1475-1508.
Author URL.
2021
Loisel J, Gallego-Sala AV, Amesbury MJ, Magnan G, Anshari G, Beilman DW, Benavides JC, Blewett J, Camill P, Charman DJ, et al (2021). Author Correction: Expert assessment of future vulnerability of the global peatland carbon sink (Nature Climate Change, (2021), 11, 1, (70-77), 10.1038/s41558-020-00944-0).
Nature Climate Change,
11(4).
Abstract:
Author Correction: Expert assessment of future vulnerability of the global peatland carbon sink (Nature Climate Change, (2021), 11, 1, (70-77), 10.1038/s41558-020-00944-0)
In the version of this Analysis originally published, the following affiliation for A. Lohila was missing: ‘Finnish Meteorological Institute, Climate System Research, Helsinki, Finland’. This affiliation has now been added, and subsequent affiliations renumbered accordingly, in the online versions of the Analysis.
Abstract.
Sim TG, Swindles GT, Morris PJ, Baird AJ, Cooper CL, Gallego-Sala AV, Charman DJ, Roland TP, Borken W, Mullan DJ, et al (2021). Divergent responses of permafrost peatlands to recent climate change.
Environmental Research Letters,
16(3), 034001-034001.
Abstract:
Divergent responses of permafrost peatlands to recent climate change
Abstract
. Permafrost peatlands are found in high-latitude regions and store globally-important amounts of soil organic carbon. These regions are warming at over twice the global average rate, causing permafrost thaw, and exposing previously inert carbon to decomposition and emission to the atmosphere as greenhouse gases. However, it is unclear how peatland hydrological behaviour, vegetation structure and carbon balance, and the linkages between them, will respond to permafrost thaw in a warming climate. Here we show that permafrost peatlands follow divergent ecohydrological trajectories in response to recent climate change within the same rapidly warming region (northern Sweden). Whether a site becomes wetter or drier depends on local factors and the autogenic response of individual peatlands. We find that bryophyte-dominated vegetation demonstrates resistance, and in some cases resilience, to climatic and hydrological shifts. Drying at four sites is clearly associated with reduced carbon sequestration, while no clear relationship at wetting sites is observed. We highlight the complex dynamics of permafrost peatlands and warn against an overly-simple approach when considering their ecohydrological trajectories and role as C sinks under a warming climate.
Abstract.
Sim TG, Swindles GT, Morris PJ, Baird AJ, Charman DJ, Amesbury MJ, Beilman D, Channon A, Gallego-Sala AV (2021). Ecology of peatland testate amoebae in Svalbard and the development of transfer functions for reconstructing past water-table depth and pH.
Ecological Indicators,
131Abstract:
Ecology of peatland testate amoebae in Svalbard and the development of transfer functions for reconstructing past water-table depth and pH
Peatlands are valuable archives of information about past environmental conditions and represent a globally-important carbon store. Robust proxy methods are required to reconstruct past ecohydrological dynamics in high-latitude peatlands to improve our understanding of change in these carbon-rich ecosystems. The High Arctic peatlands in Svalbard are at the northern limit of current peatland distribution and have experienced rapidly rising temperatures of 0.81 °C per decade since 1958. We examine the ecology of peatland testate amoebae in surface vegetation samples from permafrost peatlands on Spitsbergen, the largest island of the Svalbard archipelago, and develop new transfer functions to reconstruct water-table depth (WTD) and pH that can be applied to understand past peatland ecosystem dynamics in response to climate change. These transfer functions are the first of their kind for peatlands in Svalbard and the northernmost developed to date. Multivariate statistical analysis shows that WTD and pore water pH are the dominant controls on testate amoeba species distribution. This finding is consistent with results from peatlands in lower latitudes with regard to WTD and supports work showing that when samples are taken across a long enough trophic gradient, peatland trophic status is an important control on the distribution of testate amoebae. No differences were found between transfer functions including and excluding the taxa with weak idiosomic tests (WISTs) that are most susceptible to decay. The final models for application to fossil samples therefore excluded these taxa. The WTD transfer function demonstrates the best performance (R2LOO = 0.719, RMSEPLOO = 3.2 cm), but the pH transfer function also performs well (R2LOO = 0.690, RMSEPLOO = 0.320). The transfer functions were applied to a core from western Spitsbergen and suggest drying conditions ~1750 CE, followed by a trend of recent wetting and increasing pH from ~1920 CE. These new transfer functions allow the reconstruction of past peatland WTD and pH in Svalbard, thereby enabling a greater understanding of long-term ecohydrological dynamics in these rapidly changing ecosystems.
Abstract.
Loisel J, Gallego-Sala AV, Amesbury MJ, Magnan G, Anshari G, Beilman DW, Benavides JC, Blewett J, Camill P, Charman DJ, et al (2021). Expert assessment of future vulnerability of the global peatland carbon sink.
Nature Climate Change,
11(1), 70-77.
Abstract:
Expert assessment of future vulnerability of the global peatland carbon sink
The carbon balance of peatlands is predicted to shift from a sink to a source this century. However, peatland ecosystems are still omitted from the main Earth system models that are used for future climate change projections, and they are not considered in integrated assessment models that are used in impact and mitigation studies. By using evidence synthesized from the literature and an expert elicitation, we define and quantify the leading drivers of change that have impacted peatland carbon stocks during the Holocene and predict their effect during this century and in the far future. We also identify uncertainties and knowledge gaps in the scientific community and provide insight towards better integration of peatlands into modelling frameworks. Given the importance of the contribution by peatlands to the global carbon cycle, this study shows that peatland science is a critical research area and that we still have a long way to go to fully understand the peatland–carbon–climate nexus.
Abstract.
Qiu C, Ciais P, Zhu D, Guenet B, Peng S, Petrescu AMR, Lauerwald R, Makowski D, Gallego-Sala AV, Charman DJ, et al (2021). Large historical carbon emissions from cultivated northern peatlands.
Science Advances,
7(23).
Abstract:
Large historical carbon emissions from cultivated northern peatlands
. Crop cultivation of northern peatlands emitted large amount of CO
. 2
. over the period 850–2010.
.
Abstract.
Whittle A (2021). Late Quaternary changes in the Westerly Winds over the Southern Ocean.
Abstract:
Late Quaternary changes in the Westerly Winds over the Southern Ocean
The latitudinal position and intensity of the Southern Hemisphere westerly winds (SHW) has important and far-reaching implications for global climate and the physical environment in the southern high latitudes. Despite this, our ability to project how they will change in the future is reduced by limited understanding of their behaviour over centennial to millennial timescales. Peatland archives on the sub-Antarctic Islands are uniquely located inside the core wind-belt (50-55˚S), and hence ideally situated to reconstruct changes in westerly wind behaviour. However, suitable proxies to develop reconstructions of wind-strength throughout the region are lacking. Westerly winds are shown to enrich the sub-Antarctic Islands with salt-spray in concentrations that are proportional to wind-strength. This research has tested the potential for peat-dwelling testate amoebae to act as a bioindicator for variations in salt-spray deposition through time. Measurements of communities in variably salt-enriched environments - spanning a gradient from predominantly freshwater to salt-marsh - revealed a strong relationship between the productivity of testate amoeba communities and salinity, which allows past salt-concentrations to be inferred from sub-fossil assemblages. Presented here are two reconstructions of SHW intensity over the South Atlantic, based primarily on changes in the productivity of testate amoeba communities. The first provides a high-resolution record of the changes in wind-intensity over recent decades, extending beyond the observational record to 1920 CE, and demonstrating that present-day wind conditions are unprecedented over the last century. The second record, collected from the same site, provides a c. 8000-year reconstruction of wind-intensity over the South Atlantic, based on changes in testate amoeba productivity as part of a multi-proxy analysis that includes three independent proxies to track the deposition of salt-spray aerosols and minerogenic particles into the peat record on Bird Island (sub-Antarctica). Three significant phases of intensified winds during this period (0.45-1.15, 2.8-3.65 and 4.45-8 k yr BP) indicate long-term correspondence between temperature and wind-strength at 54˚S. These observations suggest that with climatic warming in the 21st Century, the westerly wind belt will continue to intensify and displace southwards, leading to increased wind-stress over the Southern Ocean. Implications of this shift are expected to include; reduced precipitation supply to the Southern Hemisphere continents, reduced Antarctic ice-sheet stability and increased contributions to global sea-level, and weakening of the Southern Ocean carbon sink, allowing accumulation of more CO₂ in the atmosphere.
Abstract.
Whittle A, Barnett RL, Charman DJ, Gallego‐Sala AV (2021). Low‐salinity transitions drive abrupt microbial response to sea‐level change. Ecology Letters, 25(1), 17-25.
Mackay H, Amesbury MJ, Langdon PG, Charman DJ, Magnan G, van Bellen S, Garneau M, Bainbridge R, Hughes PDM (2021). Spatial variation of hydroclimate in north-eastern North America during the last millennium.
Quaternary Science Reviews,
256Abstract:
Spatial variation of hydroclimate in north-eastern North America during the last millennium
Climatic expressions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) vary regionally, with reconstructions often depicting complex spatial patterns of temperature and precipitation change. The characterisation of these spatial patterns helps advance understanding of hydroclimate variability and associated responses of human and natural systems to climate change. Many regions, including north-eastern North America, still lack well-resolved records of past hydrological change. Here, we reconstruct hydroclimatic change over the past millennium using testate amoeba-inferred peatland water table depth reconstructions obtained from fifteen peatlands across Maine, Nova Scotia, Newfoundland and Québec. Spatial comparisons of reconstructed water table depths reveal complex hydroclimatic patterns that varied over the last millennium. The records suggest a spatially divergent pattern across the region during the Medieval Climate Anomaly and the Little Ice Age. Southern peatlands were wetter during the Medieval Climate Anomaly, whilst northern and more continental sites were drier. There is no evidence at the multi-decadal sampling resolution of this study to indicate that Medieval mega-droughts recorded in the west and continental interior of North America extended to these peatlands in the north-east of the continent. Reconstructed Little Ice Age hydroclimate change was spatially variable rather than displaying a clear directional shift or latitudinal trends, which may relate to local temporary permafrost aggradation in northern sites, and reconstructed characteristics of some dry periods during the Little Ice Age are comparable with those reconstructed during the Medieval Climate Anomaly. The spatial hydroclimatic trends identified here suggest that over the last millennium, peatland moisture balance in north-eastern North America has been influenced by changes in the Polar Jet Stream, storm activities and sea surface temperatures in the North Atlantic as well as internal peatland dynamics.
Abstract.
Mackay H, Plunkett G, Jensen B, Aubry T, Corona C, Kim WM, Toohey M, Sigl M, Stoffel M, Anchukaitis K, et al (2021). The 852/3 CE Mount Churchill eruption: examining the potential climatic and societal impacts and the timing of the Medieval Climate Anomaly in the North Atlantic Region. , 2021, 1-50.
McKeown MM, Mitchell EAD, Amesbury MJ, Blandenier Q, Charman D, Duckert C, Roland TP, Swindles GT, Wood JR, Wilmshurst JM, et al (2021). The testate amoebae of New Zealand: a checklist, identification key and assessment of biogeographic patterns. European Journal of Protistology, 81, 125789-125789.
2020
Williams M, Zhang Y, Estop-Aragonés C, Fisher JP, Xenakis G, Charman DJ, Hartley IP, Murton JB, Phoenix GK (2020). Boreal permafrost thaw amplified by fire disturbance and precipitation increases. Environmental Research Letters, 15(11), 114050-114050.
Barnett R, Charman DJ, Johns C, Ward SL, Bevan A, Bradley SL, Camidge K, Fyfe RM, Gehrels WR, Gehrels MJ, et al (2020). Datasets for: Non-linear landscape and cultural response to sea-level rise.
Abstract:
Datasets for: Non-linear landscape and cultural response to sea-level rise
Rising sea levels have been associated with human migration and behavioral shifts throughout prehistory, often with an emphasis on landscape submergence and consequent societal collapse. However, the assumption that future sea-level rise will drive similar adaptive responses is overly simplistic. Whilst the change from land to sea represents a dramatic and permanent shift for pre-existing human populations, the process of change is driven by a complex set of physical and cultural processes with long transitional phases of landscape and socio-economic change. Here we use reconstructions of prehistoric sea-level rise, paleogeographies, terrestrial landscape change and human population dynamics to show how the gradual inundation of an island archipelago resulted in decidedly non-linear landscape and cultural responses to rising sea-levels. Interpretation of past and future responses to sea-level change requires a better understanding of local physical and societal contexts to assess plausible human response patterns in the future.
Abstract.
Barnett RL, Charman DJ, Johns C, Ward SL, Bevan A, Bradley SL, Camidge K, Fyfe RM, Gehrels WR, Gehrels MJ, et al (2020). Nonlinear landscape and cultural response to sea-level rise.
Science Advances,
6(45).
Abstract:
Nonlinear landscape and cultural response to sea-level rise
Past landscape change and human response to rising sea levels in island settings are shown to be nonlinear.
Abstract.
2019
Barnett RL, Bernatchez P, Garneau M, Brain MJ, Charman DJ, Stephenson DB, Haley S, Sanderson N (2019). Late Holocene sea-level changes in eastern Quebec and potential drivers.
QUATERNARY SCIENCE REVIEWS,
203, 151-169.
Author URL.
Young DM, Baird AJ, Charman DJ, Evans CD, Gallego-Sala AV, Gill PJ, Hughes PDM, Morris PJ, Swindles GT (2019). Misinterpreting carbon accumulation rates in records from near-surface peat.
Sci Rep,
9(1).
Abstract:
Misinterpreting carbon accumulation rates in records from near-surface peat.
Peatlands are globally important stores of carbon (C) that contain a record of how their rates of C accumulation have changed over time. Recently, near-surface peat has been used to assess the effect of current land use practices on C accumulation rates in peatlands. However, the notion that accumulation rates in recently formed peat can be compared to those from older, deeper, peat is mistaken - continued decomposition means that the majority of newly added material will not become part of the long-term C store. Palaeoecologists have known for some time that high apparent C accumulation rates in recently formed peat are an artefact and take steps to account for it. Here we show, using a model, how the artefact arises. We also demonstrate that increased C accumulation rates in near-surface peat cannot be used to infer that a peatland as a whole is accumulating more C - in fact the reverse can be true because deep peat can be modified by events hundreds of years after it was formed. Our findings highlight that care is needed when evaluating recent C addition to peatlands especially because these interpretations could be wrongly used to inform land use policy and decisions.
Abstract.
Author URL.
Newnham RM, Hazell ZJ, Charman DJ, Lowe DJ, Rees ABH, Amesbury MJ, Roland TP, Gehrels M, van den Bos V, Jara IA, et al (2019). Peat humification records from Restionaceae bogs in northern New Zealand as potential indicators of Holocene precipitation, seasonality, and ENSO.
Quaternary Science Reviews,
218, 378-394.
Abstract:
Peat humification records from Restionaceae bogs in northern New Zealand as potential indicators of Holocene precipitation, seasonality, and ENSO
In comparison with temperature reconstructions, New Zealand proxy records for paleo-precipitation are rare, despite the importance of precipitation in contemporary climate variability and for projected climate impacts. In this study, records of mid-late Holocene palaeomoisture variation were derived for two hydrologically separate ombrotrophic Restionaceae bogs in northern New Zealand, based on peat humification analysis. At each site, three cores were analysed for peat humification, facilitating both intra- and inter-site comparisons. Age models for the six sequences were developed using radiocarbon dating and tephrochronology. Twelve tephras (including six cryptotephras) were recognised, four of which were used to precisely link the two sites and to define start and end points for the records at 7027 ± 170 (Tuhua tephra) and 1718 ± 10 cal yr BP (Taupo tephra) (2σ-age ranges), respectively. We find individual differences between the six peat humification records at short-term timescales that are presumably due to local site factors, in particular changing vegetation and microtopography, or to changes in the composition of the material analysed. Stronger longer-term coherence is observed between all six records but is attributed to slow anaerobic decay over time because the implied trend towards wetter summers in the late Holocene cannot be corroborated by independent climate proxies. Despite these confounding factors, centennial scale shifts in bog surface wetness are a pervasive feature of all six records with varying degrees of overlap in time that show strong correspondence with El Niño-Southern Oscillation reconstructions from the eastern equatorial Pacific. These results indicate the potential for peat humification records from New Zealand's ombrotrophic bogs to elucidate past climate variability and also demonstrate the importance of developing multiple well-dated profiles from more than one site.
Abstract.
Whittle A, Amesbury MJ, Charman DJ, Hodgson DA, Perren BB, Roberts SJ, Gallego-Sala AV (2019). Salt-Enrichment Impact on Biomass Production in a Natural Population of Peatland Dwelling Arcellinida and Euglyphida (Testate Amoebae).
Microb Ecol,
78(2), 534-538.
Abstract:
Salt-Enrichment Impact on Biomass Production in a Natural Population of Peatland Dwelling Arcellinida and Euglyphida (Testate Amoebae).
Unicellular free-living microbial eukaryotes of the order Arcellinida (Tubulinea; Amoebozoa) and Euglyphida (Cercozoa; SAR), commonly termed testate amoebae, colonise almost every freshwater ecosystem on Earth. Patterns in the distribution and productivity of these organisms are strongly linked to abiotic conditions-particularly moisture availability and temperature-however, the ecological impacts of changes in salinity remain poorly documented. Here, we examine how variable salt concentrations affect a natural community of Arcellinida and Euglyphida on a freshwater sub-Antarctic peatland. We principally report that deposition of wind-blown oceanic salt-spray aerosols onto the peatland surface corresponds to a strong reduction in biomass and to an alteration in the taxonomic composition of communities in favour of generalist taxa. Our results suggest novel applications of this response as a sensitive tool to monitor salinisation of coastal soils and to detect salinity changes within peatland palaeoclimate archives. Specifically, we suggest that these relationships could be used to reconstruct millennial scale variability in salt-spray deposition-a proxy for changes in wind-conditions-from sub-fossil communities of Arcellinida and Euglyphida preserved in exposed coastal peatlands.
Abstract.
Author URL.
Swindles GT, Morris PJ, Mullan DJ, Payne RJ, Roland TP, Amesbury MJ, Lamentowicz M, Turner TE, Gallego-Sala A, Sim T, et al (2019). Widespread drying of European peatlands in recent centuries. Nature Geoscience, 12(11), 922-928.
2018
Zhang H, Gallego-Sala AV, Amesbury MJ, Charman DJ, Piilo SR, Valiranta MM (2018). Inconsistent Response of Arctic Permafrost Peatland Carbon Accumulation to Warm Climate Phases.
GLOBAL BIOGEOCHEMICAL CYCLES,
32(10), 1605-1620.
Author URL.
Gallego-Sala AV, Charman DJ, Brewer S, Page SE, Prentice IC, Friedlingstein P, Moreton S, Amesbury MJ, Beilman DW, Bjorck S, et al (2018). Latitudinal limits to the predicted increase of the peatland carbon sink with warming.
NATURE CLIMATE CHANGE,
8(10), 907-+.
Author URL.
Estop-Aragonés C, Cooper MDA, Fisher JP, Thierry A, Garnett MH, Charman DJ, Murton JB, Phoenix GK, Treharne R, Sanderson NK, et al (2018). Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands.
Soil Biology and Biochemistry,
118, 115-129.
Abstract:
Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands
Permafrost stores globally significant amounts of carbon (C) which may start to decompose and be released to the atmosphere in form of carbon dioxide (CO2) and methane (CH4) as global warming promotes extensive thaw. This permafrost carbon feedback to climate is currently considered to be the most important carbon-cycle feedback missing from climate models. Predicting the magnitude of the feedback requires a better understanding of how differences in environmental conditions post-thaw, particularly hydrological conditions, control the rate at which C is released to the atmosphere. In the sporadic and discontinuous permafrost regions of north-west Canada, we measured the rates and sources of C released from relatively undisturbed ecosystems, and compared these with forests experiencing thaw following wildfire (well-drained, oxic conditions) and collapsing peat plateau sites (water-logged, anoxic conditions). Using radiocarbon analyses, we detected substantial contributions of deep soil layers and/or previously-frozen sources in our well-drained sites. In contrast, no loss of previously-frozen C as CO2 was detected on average from collapsed peat plateaus regardless of time since thaw and despite the much larger stores of available C that were exposed. Furthermore, greater rates of new peat formation resulted in these soils becoming stronger C sinks and this greater rate of uptake appeared to compensate for a large proportion of the increase in CH4 emissions from the collapse wetlands. We conclude that in the ecosystems we studied, changes in soil moisture and oxygen availability may be even more important than previously predicted in determining the effect of permafrost thaw on ecosystem C balance and, thus, it is essential to monitor, and simulate accurately, regional changes in surface wetness.
Abstract.
Kemp AC, Wright AJ, Edwards RJ, Barnett RL, Brain MJ, Kopp RE, Cahill N, Horton BP, Charman DJ, Hawkes AD, et al (2018). Relative sea-level change in Newfoundland, Canada during the past ∼3000 years.
Quaternary Science Reviews,
201, 89-110.
Abstract:
Relative sea-level change in Newfoundland, Canada during the past ∼3000 years
Several processes contributing to coastal relative sea-level (RSL) change in the North Atlantic Ocean are observed and/or predicted to have distinctive spatial expressions that vary by latitude. To expand the latitudinal range of RSL records spanning the past ∼3000 years and the likelihood of recognizing the characteristic fingerprints of these processes, we reconstructed RSL at two sites (Big River and Placentia) in Newfoundland from salt-marsh sediment. Bayesian transfer functions established the height of former sea level from preserved assemblages of foraminifera and testate amoebae. Age-depth models constrained by radiocarbon dates and chronohorizons estimated the timing of sediment deposition. During the past ∼3000 years, RSL rose by ∼3.0 m at Big River and by ∼1.5 m at Placentia. A locally calibrated geotechnical model showed that post-depositional lowering through sediment compaction was minimal. To isolate and quantify contributions to RSL from global, regional linear, regional non-linear, and local-scale processes, we decomposed the new reconstructions (and those in an expanded, global database) using a spatio-temporal statistical model. The global component confirms that 20th century sea-level rise occurred at the fastest, century-scale rate in over 3000 years (P > 0.999). Distinguishing the contributions from local and regional non-linear processes is made challenging by a sparse network of reconstructions. However, only a small contribution from local-scale processes is necessary to reconcile RSL reconstructions and modeled RSL trends. We identified three latitudinally-organized groups of sites that share coherent regional non-linear trends and indicate that dynamic redistribution of ocean mass by currents and/or winds was likely an important driver of sea-level change in the North Atlantic Ocean during the past ∼3000 years.
Abstract.
Charman DJ, Amesbury MJ, Roland TP, Royles J, Hodgson DA, Convey P, Griffiths H (2018). Spatially coherent late Holocene Antarctic Peninsula surface air temperature variability.
Geology,
46(12), 1071-1074.
Abstract:
Spatially coherent late Holocene Antarctic Peninsula surface air temperature variability
The Antarctic Peninsula experienced a rapid rise in regional temperature during the second half of the 20th century, but the regional pattern of multi-centennial temperature changes and their dynamical drivers remain poorly understood. Here we use proxies of biological productivity in rare, deep moss banks to infer past surface air temperature changes on the Antarctic Peninsula and identify the drivers of these changes. Late Holocene temperatures are broadly consistent between the low-elevation moss bank records and a high-elevation ice core site, and we conclude that variation in the strength of the westerlies, linked to the Southern Annular Mode, is the most likely driver. Our data do not support a hypothesized persistent temperature dipole over the Antarctic Peninsula related to a strong influence of El Niño-Southern Oscillation. Rates of change in biological productivity on the peninsula over the 20th century are unusual in the context of the late Holocene, and further warming will drive rapid future increases in moss growth and microbial populations.
Abstract.
Zhang H, Väliranta M, Amesbury MJ, Charman DJ, Laine A, Tuittila E-S (2018). Successional change of testate amoeba assemblages along a space-for-time sequence of peatland development.
Eur J Protistol,
66, 36-47.
Abstract:
Successional change of testate amoeba assemblages along a space-for-time sequence of peatland development.
It is well established that in ombrotrophic bogs, water-table depth (WTD) is the primary environmental control on testate amoeba distribution. However, the environmental controls on testate amoebae in minerotrophic fens are less well known and successional change in their assemblages associated with fen-bog peatland development has been scarcely investigated. Here we investigate a peatland space-for-time sequence resulting from postglacial rebound on the west coast of Finland, to assess successional patterns in testate amoeba communities and their relationships with environmental variables during peatland development. Sample sites along a 10-km transect from coast to inland ranged from a recently emerged wet meadow to a mature bog. Environmental variables (e.g. peat thickness, carbon and nitrogen content, pH, WTD and vegetation) were measured alongside testate amoeba samples. Results showed that even though the distribution of testate amoebae was to some extent determined by the succession stage, many taxa had wide WTD and pH ranges. The primary environmental control for many taxa changed along the succession. In conclusion, the ecological constraints on testate amoebae in minerotrophic systems are more complex than in bogs. The detected patterns also complicate the use of testate amoebae as a primary proxy in palaeoecological reconstructions where fen-to-bog shifts occur.
Abstract.
Author URL.
Zhang H, Piilo SR, Amesbury MJ, Charman DJ, Gallego-Sala AV, Väliranta MM (2018). The role of climate change in regulating Arctic permafrost peatland hydrological and vegetation change over the last millennium.
Quaternary Science Reviews,
182, 121-130.
Abstract:
The role of climate change in regulating Arctic permafrost peatland hydrological and vegetation change over the last millennium
Climate warming has inevitable impacts on the vegetation and hydrological dynamics of high-latitude permafrost peatlands. These impacts in turn determine the role of these peatlands in the global biogeochemical cycle. Here, we used six active layer peat cores from four permafrost peatlands in Northeast European Russia and Finnish Lapland to investigate permafrost peatland dynamics over the last millennium. Testate amoeba and plant macrofossils were used as proxies for hydrological and vegetation changes. Our results show that during the Medieval Climate Anomaly (MCA), Russian sites experienced short-term permafrost thawing and this induced alternating dry-wet habitat changes eventually followed by desiccation. During the Little Ice Age (LIA) both sites generally supported dry-hummock habitats, at least partly driven by permafrost aggradation. However, proxy data suggest that occasionally, MCA habitat conditions were drier than during the LIA, implying that evapotranspiration may create important additional eco-hydrological feedback mechanisms under warm conditions. All sites showed a tendency towards dry conditions as inferred from both proxies starting either from ca. 100 years ago or in the past few decades after slight permafrost thawing, suggesting that recent warming has stimulated surface desiccation rather than deeper permafrost thawing. This study shows links between two important controls over hydrology and vegetation changes in high-latitude peatlands: direct temperature-induced surface layer response and deeper permafrost layer-related dynamics. These data provide important backgrounds for predictions of Arctic permafrost peatlands and related feedback mechanisms. Our results highlight the importance of increased evapotranspiration and thus provide an additional perspective to understanding of peatland-climate feedback mechanisms.
Abstract.
Amesbury MJ, Booth RK, Roland TP, Bunbury J, Clifford MJ, Charman DJ, Elliot S, Finkelstein S, Garneau M, Hughes PDM, et al (2018). Towards a Holarctic synthesis of peatland testate amoeba ecology: Development of a new continental-scale palaeohydrological transfer function for North America and comparison to European data.
Quaternary Science Reviews,
201, 483-500.
Abstract:
Towards a Holarctic synthesis of peatland testate amoeba ecology: Development of a new continental-scale palaeohydrological transfer function for North America and comparison to European data
Fossil testate amoeba assemblages have been used to reconstruct peatland palaeohydrology for more than two decades. While transfer function training sets are typically of local-to regional-scale in extent, combining those data to cover broad ecohydrological gradients, from the regional-to continental- and hemispheric-scales, is useful to assess if ecological optima of species vary geographically and therefore may have also varied over time. Continental-scale transfer functions can also maximise modern analogue quality without losing reconstructive skill, providing the opportunity to contextualise understanding of purely statistical outputs with greater insight into the biogeography of organisms. Here, we compiled, at moderate taxonomic resolution, a dataset of nearly 2000 modern surface peatland testate amoeba samples from 137 peatlands throughout North America. We developed transfer functions using four model types, tested them statistically and applied them to independent palaeoenvironmental data. By subdividing the dataset into eco-regions, we examined biogeographical patterns of hydrological optima and species distribution across North America. We combined our new dataset with data from Europe to create a combined transfer function. The performance of our North-American transfer function was equivalent to published models and reconstructions were comparable to those developed using regional training sets. The new model can therefore be used as an effective tool to reconstruct peatland palaeohydrology throughout the North American continent. Some eco-regions exhibited lower taxonomic diversity and some key indicator taxa had restricted ranges. However, these patterns occurred against a background of general cosmopolitanism, at the moderate taxonomic resolution used. Likely biogeographical patterns at higher taxonomic resolution therefore do not affect transfer function performance. Output from the combined North American and European model suggested that any geographical limit of scale beyond which further compilation of peatland testate amoeba data would not be valid has not yet been reached, therefore advocating the potential for a Holarctic synthesis of peatland testate amoeba data. Extending data synthesis to the tropics and the Southern Hemisphere would be more challenging due to higher regional endemism in those areas.
Abstract.
2017
Swindles GT, Morris PJ, Whitney B, Galloway JM, Gałka M, Gallego-Sala AV, Macumber AL, Mullan D, Smith MW, Amesbury MJ, et al (2017). Ecosystem state shifts during long-term development of an Amazonian peatland.
Global Change BiologyAbstract:
Ecosystem state shifts during long-term development of an Amazonian peatland
The most carbon (C) dense ecosystems of Amazonia are areas characterised by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here we present an investigation into long-term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation c. 8.9 ka BP), and developed in three stages; (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since c. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (c. 6.6-6.1 and c. 4.9-3.9 ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland – forest swamp – peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on c. 1.8-1.1 ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.
Abstract.
Grosvenor MJ, Jones RT, Turney CSM, Charman DJ, Hogg A, Coward D, Wilson R (2017). Human activity was a major driver of the mid-Holocene vegetation change in southern Cumbria: implications for the elm decline in the British Isles.
Journal of Quaternary Science,
32(7), 934-945.
Abstract:
Human activity was a major driver of the mid-Holocene vegetation change in southern Cumbria: implications for the elm decline in the British Isles
The dramatic decline in elm (Ulmus) across a large swathe of north-west Europe in the mid-Holocene has been ascribed to a number of possible factors, including climate change, human activity and/or pathogens. A major limitation for identifying the underlying cause(s) has been the limited number of high-resolution records with robust geochronological frameworks. Here, we report a multiproxy study of an upland (Blea Tarn) and lowland (Urswick Tarn) landscape in southern Cumbria (British Isles) to reconstruct vegetation change across the elm decline in an area with a rich and well-dated archaeological record to disentangle different possible controls. Here we find a two-stage decline in Ulmus taking place between 6350–6150 and 6050–5850 cal a BP, with the second phase coinciding with an intensification of human activity. The scale of the decline and associated human impact is more abrupt in the upland landscape. We consider it likely that a combination of human impact and disease drove the Ulmus decline within southern Cumbria.
Abstract.
Cooper MDA, Estop-Aragones C, Fisher JP, Thierry A, Garnett MH, Charman DJ, Murton JB, Phoenix GK, Treharne R, Kokelj SV, et al (2017). Limited contribution of permafrost carbon to
methane release from thawing peatlands. Nature Climate Change, 7, 507-511.
Orme LC, Charman DJ, Reinhardt L, Jones RT, Mitchell FJG, Stefanini BS, Barkwith A, Ellis MA, Grosvenor M (2017). Past changes in the North Atlantic storm track driven by insolation and sea-ice forcing. Geology, 45(4), 335-338.
Barnett RL, Newton TL, Charman DJ, Gehrels WR (2017). Salt-marsh testate amoebae as precise and widespread indicators of sea-level change.
EARTH-SCIENCE REVIEWS,
164, 193-207.
Author URL.
Geisen S, Mitchell EAD, Wilkinson DM, Adl S, Bonkowski M, Brown MW, Fiore-Donno AM, Heger TJ, Jassey VEJ, Krashevska V, et al (2017). Soil protistology rebooted: 30 fundamental questions to start with.
Soil Biology and Biochemistry,
111, 94-103.
Abstract:
Soil protistology rebooted: 30 fundamental questions to start with
Protists are the most diverse eukaryotes. These microbes are keystone organisms of soil ecosystems and regulate essential processes of soil fertility such as nutrient cycling and plant growth. Despite this, protists have received little scientific attention, especially compared to bacteria, fungi and nematodes in soil studies. Recent methodological advances, particularly in molecular biology techniques, have made the study of soil protists more accessible, and have created a resurgence of interest in soil protistology. This ongoing revolution now enables comprehensive investigations of the structure and functioning of soil protist communities, paving the way to a new era in soil biology. Instead of providing an exhaustive review, we provide a synthesis of research gaps that should be prioritized in future studies of soil protistology to guide this rapidly developing research area. Based on a synthesis of expert opinion we propose 30 key questions covering a broad range of topics including evolution, phylogenetics, functional ecology, macroecology, paleoecology, and methodologies. These questions highlight a diversity of topics that will establish soil protistology as a hub discipline connecting different fundamental and applied fields such as ecology, biogeography, evolution, plant-microbe interactions, agronomy, and conservation biology. We are convinced that soil protistology has the potential to be one of the most exciting frontiers in biology.
Abstract.
Roland TP, Amesbury MJ, Wilkinson DM, Charman DJ, Convey P, Hodgson DA, Royles J, Clauß S, Völcker E (2017). Taxonomic Implications of Morphological Complexity Within the Testate Amoeba Genus Corythion from the Antarctic Peninsula.
Protist,
168(5), 565-585.
Abstract:
Taxonomic Implications of Morphological Complexity Within the Testate Amoeba Genus Corythion from the Antarctic Peninsula.
Precise and sufficiently detailed morphological taxonomy is vital in biology, for example in the accurate interpretation of ecological and palaeoecological datasets, especially in polar regions, where biodiversity is poor. Testate amoebae on the Antarctic Peninsula (AP) are well-documented and variations in their population size have recently been interpreted as a proxy for microbial productivity changes in response to recent regional climate change. AP testate amoeba assemblages are dominated by a small number of globally ubiquitous taxa. We examine morphological variation in Corythion spp. across the AP, finding clear evidence supporting the presence of two morphospecies. Corythion constricta (Certes 1889) was identified on the AP for the first time and has potentially been previously misidentified. Furthermore, a southerly trend of decreasing average test size in Corythion dubium (Taránek 1881) along the AP suggests adaptive polymorphism, although the precise drivers of this remain unclear, with analysis hindered by limited environmental data. Further work into morphological variation in Corythion is needed elsewhere, alongside molecular analyses, to evaluate the potential for (pseudo)cryptic diversity within the genus. We advocate a parsimonious taxonomical approach that recognises genetic diversity but also examines and develops accurate morphological divisions and descriptions suitable for light microscopy-based ecological and palaeoecological studies.
Abstract.
Author URL.
Zhang H, Amesbury MJ, Ronkainen T, Charman DJ, Gallego-Sala AV, Valiranta M (2017). Testate amoeba as palaeohydrological indicators in the permafrost peatlands of north-east European Russia and Finnish Lapland.
Journal of Quaternary ScienceAbstract:
Testate amoeba as palaeohydrological indicators in the permafrost peatlands of north-east European Russia and Finnish Lapland
To explore the use of testate amoeba for investigating the impacts of climate change on permafrost peatland hydrology, we established a new modern training set from Arctic permafrost peatlands in north-east European Russia and Finnish Lapland. Ordination analyses showed that water-table depth (WTD) was the most important control on testate amoeba distribution. We developed a new testate amoeba-based WTD transfer function and thoroughly tested it. We found that our transfer function had strong predictive power. The best- performing model was based on tolerance-downweighted weighted averaging with inverse deshrinking (R2 1⁄4 0.77, RMSEP 1⁄4 5.62 cm with leave-one-out cross validation). The new transfer function was applied to a short peat core from Arctic Russia and revealed two major hydrological shifts, which could be validated against plant macrofossil data. We also compared our model to another two models from more temperate peatlands. Comparison of the different testate amoeba datasets suggests that testate amoeba ecohydrological relationships are similar for permafrost peatlands to those in more temperate regions, but there are some differences that suggest a need for training datasets that are fully representative of permafrost peatlands.
Abstract.
Kemp AC, Wright AJ, Barnett RL, Hawkes AD, Charman DJ, Sameshima C, King AN, Mooney HC, Edwards RJ, Horton BP, et al (2017). Utility of salt-marsh foraminifera, testate amoebae and bulk-sediment δ<sup>13</sup>C values as sea-level indicators in Newfoundland, Canada.
Marine Micropaleontology,
130, 43-59.
Abstract:
Utility of salt-marsh foraminifera, testate amoebae and bulk-sediment δ13C values as sea-level indicators in Newfoundland, Canada
We investigated the utility of foraminifera, testate amoebae and bulk-sediment δ13C measurements for reconstructing Holocene relative sea level from sequences of salt-marsh sediment in Newfoundland, Canada. Modern, surface sediment was collected along transects from low to supra-tidal elevations in eastern (at Placentia) and western (at Hynes Brook and Big River) Newfoundland. Consistent with previous work, low-diversity assemblages of foraminifera display an almost binary division into a higher salt-marsh assemblage dominated by Jadammina macrescens and Balticammina pseudomacrescens and a lower salt-marsh assemblage comprised of Miliammina fusca. This pattern and composition resembles those identified at other high latitude sites with cool climates and confirms that foraminifera are sea-level indicators. The lowest occurrence of testate amoebae was at approximately mean higher high water. The composition of high salt-marsh testate amoebae assemblages (Centropyxis cassis type, Trinema spp. Tracheleuglypha dentata type, and Euglypha spp.) in Newfoundland was similar to elsewhere in the North Atlantic, but preservation bias favors removal of species with idiosomic tests over those with xenosomic tests. The mixed high salt-marsh plant community in Newfoundland results in bulk surface-sediment δ13C values that are typical of C3 plants, making them indistinguishable from freshwater sediment. Therefore we propose that the utility of this proxy for reconstructing RSL in eastern North America is restricted to the coastline between Chesapeake Bay and southern Nova Scotia. Using a simple, multi-proxy approach to establish that samples in three radiocarbon-dated sediment cores formed between the lowest occurrence of testate amoebae and the highest occurrence of foraminifera, we generated three example late Holocene sea-level index points at Hynes Brook.
Abstract.
Galka M, Szal M, Watson EJ, Gallego-Sala A, Amesbury MJ, Charman DJ, Roland TP, Turner TE, Swindles GT (2017). Vegetation Succession, Carbon Accumulation and Hydrological Change in Subarctic Peatlands, Abisko, Northern Sweden.
PERMAFROST AND PERIGLACIAL PROCESSES,
28(4), 589-604.
Author URL.
Henke LMK, Lambert FH, Charman DJ (2017). Was the Little Ice Age more or less El Niño-like than the Medieval Climate Anomaly? Evidence from hydrological. and temperature proxy data.
Climate of the Past,
13(3), 267-301.
Abstract:
Was the Little Ice Age more or less El Niño-like than the Medieval Climate Anomaly? Evidence from hydrological. and temperature proxy data
Abstract. The El Niño–Southern Oscillation (ENSO) is the most important source of global climate variability on interannual timescales and has substantial environmental and socio-economic consequences. However, it is unclear how it interacts with large-scale climate states over longer (decadal to centennial) timescales. The instrumental ENSO record is too short for analysing long-term trends and variability and climate models are unable to accurately simulate past ENSO states. Proxy data are used to extend the record, but different proxy sources have produced dissimilar reconstructions of long-term ENSO-like climate change, with some evidence for a temperature–precipitation divergence in ENSO-like climate over the past millennium, in particular during the Medieval Climate Anomaly (MCA; AD ∼ 800–1300) and the Little Ice Age (LIA; AD ∼ 1400–1850). This throws into question the stability of the modern ENSO system and its links to the global climate, which has implications for future projections. Here we use a new statistical approach using weighting based on empirical orthogonal function (EOF) to create two new large-scale reconstructions of ENSO-like climate change derived independently from precipitation proxies and temperature proxies. The method is developed and validated using model-derived pseudo-proxy experiments that address the effects of proxy dating error, resolution, and noise to improve uncertainty estimations. We find no evidence that temperature and precipitation disagree over the ENSO-like state over the past millennium, but neither do they agree strongly. There is no statistically significant difference between the MCA and the LIA in either reconstruction. However, the temperature reconstruction suffers from a lack of high-quality proxy records located in ENSO-sensitive regions, which limits its ability to capture the large-scale ENSO signal. Further expansion of the palaeo-database and improvements to instrumental, satellite, and model representations of ENSO are needed to fully resolve the discrepancies found among proxy records and establish the long-term stability of this important mode of climatic variability.
.
Abstract.
Amesbury MJ, Roland TP, Royles J, Hodgson DA, Convey P, Griffiths H, Charman DJ (2017). Widespread Biological Response to Rapid Warming on the Antarctic Peninsula.
Curr Biol,
27(11), 1616-1622.e2.
Abstract:
Widespread Biological Response to Rapid Warming on the Antarctic Peninsula.
Recent climate change on the Antarctic Peninsula is well documented [1-5], with warming, alongside increases in precipitation, wind strength, and melt season length [1, 6, 7], driving environmental change [8, 9]. However, meteorological records mostly began in the 1950s, and paleoenvironmental datasets that provide a longer-term context to recent climate change are limited in number and often from single sites [7] and/or discontinuous in time [10, 11]. Here we use moss bank cores from a 600-km transect from Green Island (65.3°S) to Elephant Island (61.1°S) as paleoclimate archives sensitive to regional temperature change, moderated by water availability and surface microclimate [12, 13]. Mosses grow slowly, but cold temperatures minimize decomposition, facilitating multi-proxy analysis of preserved peat [14]. Carbon isotope discrimination (Δ13C) in cellulose indicates the favorability of conditions for photosynthesis [15]. Testate amoebae are representative heterotrophs in peatlands [16-18], so their populations are an indicator of microbial productivity [14]. Moss growth and mass accumulation rates represent the balance between growth and decomposition [19]. Analyzing these proxies in five cores at three sites over 150 years reveals increased biological activity over the past ca. 50 years, in response to climate change. We identified significant changepoints in all sites and proxies, suggesting fundamental and widespread changes in the terrestrial biosphere. The regional sensitivity of moss growth to past temperature rises suggests that terrestrial ecosystems will alter rapidly under future warming, leading to major changes in the biology and landscape of this iconic region-an Antarctic greening to parallel well-established observations in the Arctic [20].
Abstract.
Author URL.
2016
Orme LC, Reinhardt L, Jones RT, Charman DJ, Barkwith A, Ellis MA (2016). Aeolian sediment reconstructions from the Scottish Outer Hebrides: Late Holocene storminess and the role of the North Atlantic Oscillation.
Quaternary Science Reviews,
132, 15-25.
Abstract:
Aeolian sediment reconstructions from the Scottish Outer Hebrides: Late Holocene storminess and the role of the North Atlantic Oscillation
Northern Europe can be strongly influenced by winter storms driven by the North Atlantic Oscillation (NAO), with a positive NAO index associated with greater storminess in northern Europe. However, palaeoclimate reconstructions have suggested that the NAO-storminess relationship observed during the instrumental period is not consistent with the relationship over the last millennium, especially during the Little Ice Age (LIA), when it has been suggested that enhanced storminess occurred during a phase of persistent negative NAO. To assess this relationship over a longer time period, a storminess reconstruction from an NAO-sensitive area (the Outer Hebrides) is compared with Late Holocene NAO reconstructions. The patterns of storminess are inferred from aeolian sand deposits within two ombrotrophic peat bogs, with multiple cores and two locations used to distinguish the storminess signal from intra-site variability and local factors. The results suggest storminess increased after 1000 cal yrs BP, with higher storminess during the Medieval Climate Anomaly (MCA) than the LIA, supporting the hypothesis that the NAO-storminess relationship was consistent with the instrumental period. However the shift from a predominantly negative to positive NAO at c.2000 cal yrs BP preceded the increased storminess by 1000 years. We suggest that the long-term trends in storminess were caused by insolation changes, while oceanic forcing may have influenced millennial variability.
Abstract.
Jones JM, Gille ST, Goosse H, Abram NJ, Canziani PO, Charman DJ, Clem KR, Crosta X, De Lavergne C, Eisenman I, et al (2016). Assessing recent trends in high-latitude Southern Hemisphere surface climate.
Nature Climate Change,
6(10), 917-926.
Abstract:
Assessing recent trends in high-latitude Southern Hemisphere surface climate
Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. Most observed trends, however, are not unusual when compared with Antarctic palaeoclimate records of the past two centuries. With the exception of the positive trend in the Southern Annular Mode, climate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response.
Abstract.
Gallego-Sala AV, Charman DJ, Harrison SP, Li G, Prentice IC (2016). Climate-driven expansion of blanket bogs in Britain during the Holocene.
Climate of the Past,
12(1), 129-136.
Abstract:
Climate-driven expansion of blanket bogs in Britain during the Holocene
Blanket bog occupies approximately 6 % of the area of the UK today. The Holocene expansion of this hyperoceanic biome has previously been explained as a consequence of Neolithic forest clearance. However, the present distribution of blanket bog in Great Britain can be predicted accurately with a simple model (PeatStash) based on summer temperature and moisture index thresholds, and the same model correctly predicts the highly disjunct distribution of blanket bog worldwide. This finding suggests that climate, rather than land-use history, controls blanket-bog distribution in the UK and everywhere else. We set out to test this hypothesis for blanket bogs in the UK using bioclimate envelope modelling compared with a database of peat initiation age estimates. We used both pollen-based reconstructions and climate model simulations of climate changes between the mid-Holocene (6000 yr BP, 6 ka) and modern climate to drive PeatStash and predict areas of blanket bog. We compiled data on the timing of blanket-bog initiation, based on 228 age determinations at sites where peat directly overlies mineral soil. The model predicts that large areas of northern Britain would have had blanket bog by 6000 yr BP, and the area suitable for peat growth extended to the south after this time. A similar pattern is shown by the basal peat ages and new blanket bog appeared over a larger area during the late Holocene, the greatest expansion being in Ireland, Wales, and southwest England, as the model predicts. The expansion was driven by a summer cooling of about 2 °C, shown by both pollen-based reconstructions and climate models. The data show early Holocene (pre-Neolithic) blanket-bog initiation at over half of the sites in the core areas of Scotland and northern England. The temporal patterns and concurrence of the bioclimate model predictions and initiation data suggest that climate change provides a parsimonious explanation for the early Holocene distribution and later expansion of blanket bogs in the UK, and it is not necessary to invoke anthropogenic activity as a driver of this major landscape change.
Abstract.
Amesbury MJ, Swindles GT, Bobrov A, Charman DJ, Holden J, Lamentowicz M, Mallon G, Mazei Y, Mitchell EAD, Payne RJ, et al (2016). Development of a new pan-European testate amoeba transfer function for reconstructing peatland palaeohydrology.
Quaternary Science Reviews,
152, 132-151.
Abstract:
Development of a new pan-European testate amoeba transfer function for reconstructing peatland palaeohydrology
In the decade since the first pan-European testate amoeba-based transfer function for peatland palaeohydrological reconstruction was published, a vast amount of additional data collection has been undertaken by the research community. Here, we expand the pan-European dataset from 128 to 1799 samples, spanning 35° of latitude and 55° of longitude. After the development of a new taxonomic scheme to permit compilation of data from a wide range of contributors and the removal of samples with high pH values, we developed ecological transfer functions using a range of model types and a dataset of ∼1300 samples. We rigorously tested the efficacy of these models using both statistical validation and independent test sets with associated instrumental data. Model performance measured by statistical indicators was comparable to other published models. Comparison to test sets showed that taxonomic resolution did not impair model performance and that the new pan-European model can therefore be used as an effective tool for palaeohydrological reconstruction. Our results question the efficacy of relying on statistical validation of transfer functions alone and support a multi-faceted approach to the assessment of new models. We substantiated recent advice that model outputs should be standardised and presented as residual values in order to focus interpretation on secure directional shifts, avoiding potentially inaccurate conclusions relating to specific water-table depths. The extent and diversity of the dataset highlighted that, at the taxonomic resolution applied, a majority of taxa had broad geographic distributions, though some morphotypes appeared to have restricted ranges.
Abstract.
Edward Turner T, Swindles GT, Charman DJ, Langdon PG, Morris PJ, Booth RK, Parry LE, Nichols JE (2016). Erratum: Solar cycles or random processes? Evaluating solar variability in Holocene climate records (Scientific Reports (2016) 6 (23961) DOI: 10.1038/srep23961)). Scientific Reports, 6
Orme LC, Reinhardt L, Jones RT, Charman DJ, Croudace I, Dawson A, Ellis M, Barkwith A (2016). Investigating the maximum resolution of µXRF core scanners: a 1800 year storminess reconstruction from the Outer Hebrides, Scotland, UK.
Holocene,
26(2), 235-247.
Abstract:
Investigating the maximum resolution of µXRF core scanners: a 1800 year storminess reconstruction from the Outer Hebrides, Scotland, UK
Micro x-ray fluorescence (µXRF) core scanning is capable of measuring the elemental composition of lake sediment at sub-millimetre resolution, but bioturbation and physical mixing may degrade environmental signals at such fine scales. The aim of this research is to determine the maximum possible resolution at which meaningful environmental signals may be reconstructed from lake sediments using this method. Sediment from a coastal lake in the Outer Hebrides, Scotland, has been analysed using calibrated element measurements to reconstruct storminess since AD 200. We find that a Ca/K ratio in lake-core sediments reflects the presence of fine calcium carbonate shell fragments, a constituent of sand in the catchment that is washed and blown into the lake. Variations in this ratio are significantly correlated with instrumental records of precipitation and low pressures, suggesting it is a proxy for storminess. Furthermore, identification of a c. 60-year cycle supports a climatic influence on Ca/K, as this cycle is frequently identified in reconstructions of the North Atlantic Oscillation and North Atlantic sea-surface temperature. Comparison with weather records at different resolutions and spectral analysis indicate that µXRF data from Loch Hosta can be interpreted at sub-decadal resolutions (equivalent to core depth intervals of 3–5 mm in this location). Therefore, we suggest that sub-centimetre sampling using µXRF core scanning could be beneficial in producing environmental reconstructions in many lake settings where sediments are not varved.
Abstract.
Loader NJ, Street-Perrott FA, Mauquoy D, Roland TP, van Bellen S, Daley TJ, Davies D, Hughes PDM, Pancotto VO, Young GHF, et al (2016). Measurements of hydrogen, oxygen and carbon isotope variability in Sphagnum moss along a micro-topographical gradient in a southern Patagonian peatland.
Journal of Quaternary Science,
31(4), 426-435.
Abstract:
Measurements of hydrogen, oxygen and carbon isotope variability in Sphagnum moss along a micro-topographical gradient in a southern Patagonian peatland
Peat archives offer a diverse range of physical and chemical proxies from which it is possible to study past environmental and ecological changes. Direct numerical calibration and verification is difficult so process-based and mechanistic studies are therefore required to establish and quantify links between environmental changes and their associated proxy-responses. Traditional ‘space-for-time’ calibrations provide a solution to this calibration problem, but are often unable to isolate a single environmental variable from other potentially confounding variables. In this study, we explored the potential of a site-specific ‘space-for-time’ approach applied to a hummock-hollow transect on an ombrotrophic raised bog in Patagonia, southern Chile. Coupled stable carbon, oxygen and hydrogen isotopic measurements were made on individual samples of Sphagnum moss cellulose and compared with plant-associated waters, local hydrology, temperature and relative humidity, sampled at the same points along the study transect. Results reveal a range of environmental responses, which were supported by plant-physiological models in the case of carbon and oxygen isotopes. For hydrogen isotopes, the results obtained from cellulose indicated a need for further research into hydrogen isotope fractionation in Sphagnum. We recommend conducting site-specific characterization of plant response to support the development of peat-based isotope records for palaeoenvironmental research, and where logistically possible, that monitoring is conducted over timescales appropriate to the time-integrative nature of the Sphagnum record.
Abstract.
Royles J, Amesbury MJ, Roland TP, Jones GD, Convey P, Griffiths H, Hodgson DA, Charman DJ (2016). Moss stable isotopes (carbon-13, oxygen-18) and testate amoebae reflect environmental inputs and microclimate along a latitudinal gradient on the Antarctic Peninsula.
Oecologia,
181(3), 931-945.
Abstract:
Moss stable isotopes (carbon-13, oxygen-18) and testate amoebae reflect environmental inputs and microclimate along a latitudinal gradient on the Antarctic Peninsula
The stable isotope compositions of moss tissue water (δ2H and δ18O) and cellulose (δ13C and δ18O), and testate amoebae populations were sampled from 61 contemporary surface samples along a 600-km latitudinal gradient of the Antarctic Peninsula (AP) to provide a spatial record of environmental change. The isotopic composition of moss tissue water represented an annually integrated precipitation signal with the expected isotopic depletion with increasing latitude. There was a weak, but significant, relationship between cellulose δ18O and latitude, with predicted source water inputs isotopically enriched compared to measured precipitation. Cellulose δ13C values were dependent on moss species and water content, and may reflect site exposure to strong winds. Testate amoebae assemblages were characterised by low concentrations and taxonomic diversity, with Corythion dubium and Microcorycia radiata types the most cosmopolitan taxa. The similarity between the intra- and inter-site ranges measured in all proxies suggests that microclimate and micro-topographical conditions around the moss surface were important determinants of proxy values. Isotope and testate amoebae analyses have proven value as palaeoclimatic, temporal proxies of climate change, whereas this study demonstrates that variations in isotopic and amoeboid proxies between microsites can be beyond the bounds of the current spatial variability in AP climate.
Abstract.
Gallego-Sala AV, Booth RK, Charman DJ, Prentice IC, Yu Z (2016). Peatlands and Climate Change. In Bonn A, Allott T, Evans M, Joosten H, Stoneman R (Eds.)
Peatland Restoration and Ecosystem Services
Science, Policy and Practice, Cambridge University Press.
Abstract:
Peatlands and Climate Change
Abstract.
Payne RJ, Babeshko KV, van Bellen S, Blackford JJ, Booth RK, Charman DJ, Ellershaw MR, Gilbert D, Hughes PDM, Jassey VEJ, et al (2016). Significance testing testate amoeba water table reconstructions.
Quaternary Science Reviews,
138, 131-135.
Abstract:
Significance testing testate amoeba water table reconstructions
Transfer functions are valuable tools in palaeoecology, but their output may not always be meaningful. A recently-developed statistical test ('randomTF') offers the potential to distinguish among reconstructions which are more likely to be useful, and those less so. We applied this test to a large number of reconstructions of peatland water table depth based on testate amoebae. Contrary to our expectations, a substantial majority (25 of 30) of these reconstructions gave non-significant results (P > 0.05). The underlying reasons for this outcome are unclear. We found no significant correlation between randomTF P-value and transfer function performance, the properties of the training set and reconstruction, or measures of transfer function fit. These results give cause for concern but we believe it would be extremely premature to discount the results of non-significant reconstructions. We stress the need for more critical assessment of transfer function output, replication of results and ecologically-informed interpretation of palaeoecological data.
Abstract.
Turner TE, Swindles GT, Charman DJ, Langdon PG, Morris PJ, Booth RK, Parry LE, Nichols JE (2016). Solar cycles or random processes? Evaluating solar variability in Holocene climate records.
Sci Rep,
6Abstract:
Solar cycles or random processes? Evaluating solar variability in Holocene climate records.
Many studies have reported evidence for solar-forcing of Holocene climate change across a range of archives. These studies have compared proxy-climate data with records of solar variability (e.g. (14)C or (10)Be), or have used time series analysis to test for the presence of solar-type cycles. This has led to some climate sceptics misrepresenting this literature to argue strongly that solar variability drove the rapid global temperature increase of the twentieth century. As proxy records underpin our understanding of the long-term processes governing climate, they need to be evaluated thoroughly. The peatland archive has become a prominent line of evidence for solar forcing of climate. Here we examine high-resolution peatland proxy climate data to determine whether solar signals are present. We find a wide range of significant periodicities similar to those in records of solar variability: periods between 40-100 years, and 120-140 years are particularly common. However, periodicities similar to those in the data are commonly found in random-walk simulations. Our results demonstrate that solar-type signals can be the product of random variations alone, and that a more critical approach is required for their robust interpretation.
Abstract.
Author URL.
Edvardsson J, Stoffel M, Corona C, Bragazza L, Leuschner HH, Charman DJ, Helama S (2016). Subfossil peatland trees as proxies for Holocene palaeohydrology and palaeoclimate.
Earth-Science Reviews,
163, 118-140.
Abstract:
Subfossil peatland trees as proxies for Holocene palaeohydrology and palaeoclimate
Due to the scarcity of reliable and highly resolved moisture proxies covering much of the Holocene, there has been increased interest in the study of living and subfossil peatland trees sensitive to gradual and extreme changes in hydrology, precipitation, and related environmental processes. Peatland development and the associated carbon accumulation, which are strongly influenced by hydrological fluctuations, are also of prime importance as peatlands represent long-term sinks of atmospheric carbon. Improved knowledge of peatland development and soil moisture variability during the Holocene is therefore essential to our understanding of long-term hydroclimate changes, the terrestrial carbon cycle, and to enable more robust predictions of peatland response to future climate changes. Here, we review the existing mid- to late Holocene peatland tree-ring chronologies that have been used to study climate variability on (sub-)annual to centennial scales with a primary focus on northern Europe. Since the 1970s, absolutely dated tree-ring chronologies covering substantial parts of the Holocene have been developed from excavated remains of oak (Quercus spp.) and pine (Pinus sylvestris L.). The annual tree-ring patterns of these trees are often characterized by periods of depressed growth reflecting annual to decadal hydroclimatic changes. In addition, changes in the spatio-temporal distribution of trees throughout the Holocene are often found to reflect decadal to centennial climate and hydrological changes. Moreover, synchronicity between tree-ring chronologies and tree-population dynamics over larger geographical areas show periods of coherent regional climate forcing, especially during the mid-Holocene. This review (i) provides an overview of pioneering and recent studies presenting tree-ring chronologies developed from subfossil peatland trees, and (ii) presents recent developments in the fields of dendroecology (i.e. the response of tree growth and changes in vitality as a result of changes in climatic variables) and dendroclimatology (i.e. the reconstruction of climate fluctuations based on tree-ring analyses) in peatland regions. Moreover, we (iii) use long-term climate reconstructions based on alternative proxies for comparison, and (iv) present different ways to analyse tree-ring records to generate novel information on annual to centennial timescales. This analysis is based on an unprecedented network of tree-ring chronologies from Denmark, Finland, Germany, Great Britain, Ireland, Lithuania, the Netherlands, Poland, Sweden, and Canada, as well as a wealth of old and previously (un) published literature from Scandinavia and Germany, which has not been accessible to a wider audience in the past due to inaccessibility or linguistic barriers. Finally, a map of possible hotspots for the assessment of continuous peatland-tree studies is presented, along with suggestions for new research directions in the field.
Abstract.
Fisher JP, Estop-Aragonés C, Thierry A, Charman DJ, Wolfe SA, Hartley IP, Murton JB, Williams M, Phoenix GK (2016). The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest.
Global change biology,
22(9), 3127-3140.
Abstract:
The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest
Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict future impacts of climate warming on permafrost degradation and subsequent feedback to climate.
Abstract.
2015
Amesbury MJ, Charman DJ, Newnham RM, Loader NJ, Goodrich J, Royles J, Campbell DI, Keller ED, Baisden WT, Roland TP, et al (2015). Can oxygen stable isotopes be used to track precipitation moisture source in vascular plant-dominated peatlands?.
Earth and Planetary Science Letters,
430, 149-159.
Abstract:
Can oxygen stable isotopes be used to track precipitation moisture source in vascular plant-dominated peatlands?
Variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature- and humidity-dependent phase changes associated with evaporation and condensation. Oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives, which integrate this signal over time. Applications from ombrotrophic peatlands, where the source water used in cellulose synthesis is derived solely from precipitation, have been mostly limited to Northern Hemisphere Sphagnum-dominated bogs, with few in the Southern Hemisphere or in peatlands dominated by vascular plants. New Zealand (NZ) provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out, in particular using the preserved root matrix of the restionaceous wire rush (Empodisma spp.) that forms deep Holocene peat deposits throughout the country. Furthermore, large gradients are observed in the mean isotopic composition of precipitation across NZ, caused primarily by the relative influence of different climate modes. Here, we test whether δ18O of Empodisma α-cellulose from ombrotrophic restiad peatlands in NZ can provide a methodology for developing palaeoclimate records of past precipitation δ18O. Surface plant, water and precipitation samples were taken over spatial (six sites spanning >10° latitude) and temporal (monthly measurements over one year) gradients. A link between the isotopic composition of root-associated water, the most likely source water for plant growth, and precipitation in both datasets was found. Back-trajectory modelling of precipitation moisture source for rain days prior to sampling showed clear seasonality in the temporal data that was reflected in root-associated water. The link between source water and plant cellulose was less clear, although mechanistic modelling predicted mean cellulose values within published error margins for both datasets. Improved physiological understanding and modelling of δ18O in restiad peatlands should enable use of this approach as a new source of palaeoclimate data to reconstruct changes in past atmospheric circulation.
Abstract.
Amesbury MJ, Charman DJ, Newnham RM, Loader NJ, Goodrich JP, Royles J, Campbell DI, Roland TP, Gallego-Sala A (2015). Carbon stable isotopes as a palaeoclimate proxy in vascular plant dominated peatlands.
Geochimica et Cosmochimica Acta,
164, 161-174.
Abstract:
Carbon stable isotopes as a palaeoclimate proxy in vascular plant dominated peatlands
Carbon stable isotope (δ13C) records from vascular plant dominated peatlands have been used as a palaeoclimate proxy, but a better empirical understanding of fractionation processes in these ecosystems is required. Here, we test the potential of δ13C analysis of ombrotrophic restiad peatlands in New Zealand, dominated by the wire rush (Empodisma spp.), to provide a methodology for developing palaeoclimatic records. We took surface plant samples alongside measurements of water table depth and (micro)climate over spatial (six sites spanning>10° latitude) and temporal (monthly measurements over 1year) gradients and analysed the relationships between cellulose δ13C values and environmental parameters. We found strong, significant negative correlations between δ13C and temperature, photosynthetically active radiation and growing degree days above 0°C. No significant relationships were observed between δ13C and precipitation, relative humidity, soil moisture or water table depth, suggesting no growing season water limitation and a decoupling of the expected link between δ13C in vascular plants and hydrological variables. δ13C of Empodisma spp. roots may therefore provide a valuable temperature proxy in a climatically sensitive region, but further physiological and sub-fossil calibration studies are required to fully understand the observed signal.
Abstract.
Xing W, Bao K, Gallego-Sala AV, Charman DJ, Zhang Z, Gao C, Lu X, Wang G (2015). Climate Controls on carbon accumulation in peatlands of Northeast China.
Quaternary Science Reviews,
115, 78-88.
Abstract:
Climate Controls on carbon accumulation in peatlands of Northeast China
Peatlands contain around one third of the global soil carbon (C) and play an important role in the C cycle. In particular, the response of the productivity-decay balance to climate variability is critical for understanding both the past and future global C cycle. Most studies of peatland C dynamics have been carried out on boreal and subarctic peatlands, where climate models predict a greater increase in temperature compared to the global average. Less is known about peatlands at lower latitudes, yet there are significant peatland C stocks in these regions that may be more vulnerable to future climate change because they are closer to the climatic limit of peatland distribution. Northeast China is China's largest wetland region, with extensive peatlands in mountain regions and across the plains. Here, we used core data from 134 peatland sites to quantify the C accumulation rate over different timescales and estimate C storage across northeast China. The results show that the Holocene long-term apparent rate of C accumulation (LORCA) ranged from 5.74 to 129.31 g C m−2 yr−1, with a mean rate of 33.66 g C m−2 yr−1. The total wetland area and C storage within this region is 82,870 km2 and 4.34 Gt C, and about 80% of the C is contained in mountain peatlands. We find that total C accumulated over the last 2000 years is linearly related to photosynthetically active radiation over the growing season, supporting the hypothesis that rates of net primary productivity (NPP) are more important than decomposition rates in determining long-term C accumulation. Although peatlands in northeast China are close to the southern limit of major peatland extent, our data suggest that future warming will lead to greater future C accumulation, as long as moisture balance or cloudiness do not become limiting factors.
Abstract.
Gallego-Sala AV, Charman DJ, Harrison SP, Li G, Prentice IC (2015). Climate-driven expansion of blanket bogs in Britain during the Holocene.
Clim. Past Discuss.,
11, 4811-4832.
Abstract:
Climate-driven expansion of blanket bogs in Britain during the Holocene
Blanket bog occupies approximately 6 % of the area of the UK today. The Holocene expansion of this hyperoceanic biome has previously been explained as a consequence of Neolithic forest clearance. However, the present distribution of blanket bog in Great Britain can be predicted accurately with a simple model (PeatStash) based on summer temperature and moisture index thresholds, and the same model correctly predicts the highly disjunct distribution of blanket bog worldwide. This finding suggests that climate, rather than land-use history, controls blanket-bog distribution in the UK and everywhere else.
We set out to test this hypothesis for blanket bogs in the UK using bioclimate envelope modelling compared with a database of peat initiation age estimates. We used both pollen-based reconstructions and climate model simulations of climate changes between the mid-Holocene (6000 yr BP, 6 ka) and modern climate to drive PeatStash and predict areas of blanket bog. We compiled data on the timing of blanket-bog initiation, based on 228 age determinations at sites where peat directly overlies mineral soil. The model predicts large areas of northern Britain would have had blanket bog by 6000 yr BP, and the area suitable for peat growth extended to the south after this time. A similar pattern is shown by the basal peat ages and new blanket bog appeared over a larger area during the late Holocene, the greatest expansion being in Ireland, Wales and southwest England, as the model predicts. The expansion was driven by a summer cooling of about 2 °C, shown by both pollen-based reconstructions and climate models. The data show early Holocene (pre-Neolithic) blanket-bog initiation at over half of the sites in the core areas of Scotland, and northern England.
The temporal patterns and concurrence of the bioclimate model predictions and initiation data suggest that climate change provides a parsimonious explanation for the early Holocene distribution and later expansion of blanket bogs in the UK, and it is not necessary to invoke anthropogenic activity as a driver of this major landscape change.
Abstract.
Davies H, Fyfe R, Charman D (2015). Does peatland drainage damage the palaeoecological record?.
Review of Palaeobotany and Palynology,
221, 92-105.
Abstract:
Does peatland drainage damage the palaeoecological record?
Upland peatlands in the UK are important sources of palaeoenvironmental information, providing context to human land use in upland areas. Land management practices, particularly over the last 150. years have resulted in damage to the integrity of this palaeoenvironmental record. This study focuses on the effects of drainage on the condition of pollen remains within upland peat deposits using a case study from Exmoor, southwest England. Water-table monitoring and coring across three mires enabled the effects of water-table draw-down on the condition of pollen remains within the peat matrix to be assessed. Our results show that peatland drainage, which has taken place over the last 60-150. years, caused significant localised water-table draw-down. A detailed pollen condition survey across seven coring sites demonstrates that pollen within the peat is damaged as a consequence. However, pollen is rarely so damaged that counted pollen assemblages are unreliable. Correspondence between pollen condition and past climate shifts and periods of enhanced human activity, suggests that recent damage to pollen caused by peatland drainage is superimposed on damage caused by other factors throughout the period of peat accumulation.
Abstract.
Charman DJ, Amesbury MJ, Hinchliffe W, Hughes PDM, Mallon G, Blake WH, Daley TJ, Gallego-Sala AV, Mauquoy D (2015). Drivers of Holocene peatland carbon accumulation across a climate gradient in northeastern North America.
Quaternary Science Reviews,
121, 110-119.
Abstract:
Drivers of Holocene peatland carbon accumulation across a climate gradient in northeastern North America
Peatlands are an important component of the Holocene global carbon (C) cycle and the rate of C sequestration and storage is driven by the balance between net primary productivity and decay. A number of studies now suggest that climate is a key driver of peatland C accumulation at large spatial scales and over long timescales, with warmer conditions associated with higher rates of C accumulation. However, other factors are also likely to play a significant role in determining local carbon accumulation rates and these may modify past, present and future peatland carbon sequestration. Here, we test the importance of climate as a driver of C accumulation, compared with hydrological change, fire, nitrogen content and vegetation type, from records of C accumulation at three sites in northeastern North America, across the N-S climate gradient of raised bog distribution. Radiocarbon age models, bulk density values and %C measurements from each site are used to construct C accumulation histories commencing between 11,200 and 8000cal. years BP. The relationship between C accumulation and environmental variables (past water table depth, fire, peat forming vegetation and nitrogen content) is assessed with linear and multivariate regression analyses. Differences in long-term rates of carbon accumulation between sites support the contention that a warmer climate with longer growing seasons results in faster rates of long-term carbon accumulation. However, mid-late Holocene accumulation rates show divergent trends, decreasing in the north but rising in the south. We hypothesise that sites close to the moisture threshold for raised bog distribution increased their growth rate in response to a cooler climate with lower evapotranspiration in the late Holocene, but net primary productivity declined over the same period in northern areas causing a decrease in C accumulation. There was no clear relationship between C accumulation and hydrological change, vegetation, nitrogen content or fire, but early successional stages of peatland growth had faster rates of C accumulation even though temperatures were probably lower at the time. We conclude that climate is the most important driver of peatland accumulation rates over millennial timescales, but that successional vegetation change is a significant additional influence. Whilst the majority of northern peatlands are likely to increase C accumulation rates under future warmer climates, those at the southern limit of distribution may show reduced rates. However, early succession peatlands that develop under future warming at the northern limits of peatland distribution are likely to have high rates of C accumulation and will compensate for some of the losses elsewhere.
Abstract.
Charman DJ, Duller GAT, Long AJ, Schreve DC, Scourse JD (2015). Editorial: Quaternary revolutions. Journal of Quaternary Science, 30(2), 101-103.
Swindles GT, Amesbury MJ, Turner TE, Carrivick JL, Woulds C, Raby C, Mullan D, Roland TP, Galloway JM, Parry L, et al (2015). Evaluating the use of testate amoebae for palaeohydrological reconstruction in permafrost peatlands.
Palaeogeography, Palaeoclimatology, Palaeoecology,
424, 111-122.
Abstract:
Evaluating the use of testate amoebae for palaeohydrological reconstruction in permafrost peatlands
The melting of high-latitude permafrost peatlands is a major concern due to a potential positive feedback on global climate change. We examine the ecology of testate amoebae in permafrost peatlands, based on sites in Sweden (~200km north of the Arctic Circle). Multivariate statistical analysis confirms that water-table depth and moisture content are the dominant controls on the distribution of testate amoebae, corroborating the results from studies in mid-latitude peatlands. We present a new testate amoeba-based water table transfer function and thoroughly test it for the effects of spatial autocorrelation, clustered sampling design and uneven sampling gradients. We find that the transfer function has good predictive power; the best-performing model is based on tolerance-downweighted weighted averaging with inverse deshrinking (performance statistics with leave-one-out cross validation: R2=0.87, RMSEP=5.25cm). The new transfer function was applied to a short core from Stordalen mire, and reveals a major shift in peatland ecohydrology coincident with the onset of the Little Ice Age (c. AD 1400). We also applied the model to an independent contemporary dataset from Stordalen and find that it outperforms predictions based on other published transfer functions. The new transfer function will enable palaeohydrological reconstruction from permafrost peatlands in Northern Europe, thereby permitting greatly improved understanding of the long-term ecohydrological dynamics of these important carbon stores as well as their responses to recent climate change.
Abstract.
Summerhayes C, Charman D (2015). Introduction to holocene climate change: New perspectives. Journal of the Geological Society, 172(2), 251-253.
Barnett RL, Gehrels WR, Charman DJ, Saher MH, Marshall WA (2015). Late Holocene sea-level change in Arctic Norway.
Quaternary Science Reviews,
107, 214-230.
Abstract:
Late Holocene sea-level change in Arctic Norway
Relative sea-level data from the pre-industrial era are required for validating geophysical models of glacio-isostatic adjustment as well as for testing models used to make sea-level predictions based on future climate change scenarios. We present the first late Holocene (past ~3300 years) relative sea-level reconstruction for northwestern Norway based on investigations in South Hinnøya in the Vesterålen - Lofoton archipelago. Sea-level changes are reconstructed from analyses of salt-marsh and estuarine sediments and the micro-organisms (foraminifera and testate amoebae) preserved within. The 'indicative meaning' of the microfauna is established from their modern distributions. Records are dated by radiocarbon, 201Pb, 137Cs and chemostratigraphical analyses. Our results show a continuous relative sea-level decline of 0.7-0.9mmyr-1 for South Hinnøya during the late Holocene. The reconstruction extends the relative sea-level trend recorded by local tide gauge data which is only available for the past ~25 years. Our reconstruction demonstrates that existing models of shoreline elevations and GIA overpredict sea-level positions during the late Holocene. We suggest that models might be adjusted in order to reconcile modelled and reconstructed sea-level changes and ultimately improve understanding of GIA in Fennoscandia.
Abstract.
Perez M, Fyfe RM, Charman DJ, Gehrels WR (2015). Later Holocene vegetation history of the Isles of Scilly, UK: coastal influence and human land use in a small island context.
JOURNAL OF QUATERNARY SCIENCE,
30(8), 764-778.
Author URL.
Charman D (2015). Testate amoebae. In Shennan I, Long AJ, Horton BP (Eds.) Handbook of sea-level research, Chichester: Wiley, 281-294.
Swindles GT, Holden J, Raby CL, Turner TE, Blundell A, Charman DJ, Menberu MW, Kløve B (2015). Testing peatland water-table depth transfer functions using high-resolution hydrological monitoring data.
Quaternary Science Reviews,
120, 107-117.
Abstract:
Testing peatland water-table depth transfer functions using high-resolution hydrological monitoring data
Transfer functions are now commonly used to reconstruct past environmental variability from palaeoecological data. However, such approaches need to be critically appraised. Testate amoeba-based transfer functions are an established method for the quantitative reconstruction of past water-table variations in peatlands, and have been applied to research questions in palaeoclimatology, peatland ecohydrology and archaeology. We analysed automatically-logged peatland water-table data from dipwells located in England, Wales and Finland and a suite of three year, one year and summer water-table statistics were calculated from each location. Surface moss samples were extracted from beside each dipwell and the testate amoebae community composition was determined. Two published transfer functions were applied to the testate-amoeba data for prediction of water-table depth (England and Europe). Our results show that estimated water-table depths based on the testate amoeba community reflect directional changes, but that they are poor representations of the real mean or median water-table magnitudes for the study sites. We suggest that although testate amoeba-based reconstructions can be used to identify past shifts in peat hydrology, they cannot currently be used to establish precise hydrological baselines such as those needed to inform management and restoration of peatlands. One approach to avoid confusion with contemporary water-table determinations is to use residuals or standardised values for peatland water-table reconstructions. We contend that our test of transfer functions against independent instrumental data sets may be more powerful than relying on statistical testing alone.
Abstract.
Roland TP, Daley TJ, Caseldine CJ, Charman DJ, Turney CSM, Amesbury MJ, Thompson GJ, Woodley EJ (2015). The 5.2 ka climate event: Evidence from stable isotope and multi-proxy palaeoecological peatland records in Ireland.
Quaternary Science Reviews,
124, 209-223.
Abstract:
The 5.2 ka climate event: Evidence from stable isotope and multi-proxy palaeoecological peatland records in Ireland
Evidence for a major climate event at 5.2 ka has been reported globally and is associated with considerable societal disruption, but is poorly characterised in northwest Europe. This event forms part of a broader period of re-organisation in the Earth's ocean-atmosphere circulation system between 6 and 5 ka. This study tests the nature and timing of the event in northwest Europe, a region highly sensitive to change in meridional overturning circulation and mid-latitude westerly airflow. Here we report three high-resolution Irish multi-proxy records obtained from ombrotrophic peatlands that have robust chronological frameworks. We identify the 5.2 ka event by a sustained decrease in δ18Ocellulose at all three sites, with additional and parallel changes in δ13Ccellulose and palaeoecological (testate amoebae, plant macrofossil and humification) data from two sites in northern Ireland. Data from Sluggan Moss demonstrate a particularly coherent shift towards wetter conditions. These data support the hypothesis that the event was caused by a prolonged period of positive North Atlantic Oscillation conditions, resulting in pervasive cyclonic weather patterns across northwest Europe, increasing precipitation over Ireland.
Abstract.
Swindles GT, Morris PJ, Mullan D, Watson EJ, Turner E, Roland TP, Amesbury MJ, Kokfelt U, Schoning K, Pratte S, et al (2015). The long-term fate of permafrost peatlands under rapid climate warming.
Scientific Reports,
5Abstract:
The long-term fate of permafrost peatlands under rapid climate warming
Permafrost peatlands contain globally important amounts of soil organic carbon, owing to cold conditions which suppress anaerobic decomposition. However, climate warming and permafrost thaw threaten the stability of this carbon store. The ultimate fate of permafrost peatlands and their carbon stores is unclear because of complex feedbacks between peat accumulation, hydrology and vegetation. Field monitoring campaigns only span the last few decades and therefore provide an incomplete picture of permafrost peatland response to recent rapid warming. Here we use a high-resolution palaeoecological approach to understand the longer-term response of peatlands in contrasting states of permafrost degradation to recent rapid warming. At all sites we identify a drying trend until the late-twentieth century; however, two sites subsequently experienced a rapid shift to wetter conditions as permafrost thawed in response to climatic warming, culminating in collapse of the peat domes. Commonalities between study sites lead us to propose a five-phase model for permafrost peatland response to climatic warming. This model suggests a shared ecohydrological trajectory towards a common end point: inundated Arctic fen. Although carbon accumulation is rapid in such sites, saturated soil conditions are likely to cause elevated methane emissions that have implications for climate-feedback mechanisms.
Abstract.
Henke LMK, Lambert FH, Charman DJ (2015). Was the Little Ice Age more or less El Niño-like than the Mediaeval Climate Anomaly? Evidence from hydrological and temperature proxy data. , 11(6), 5549-5604.
2014
Loisel J, Yu Z, Beilman DW, Camill P, Alm J, Amesbury MJ, Anderson D, Andersson S, Bochicchio C, Barber K, et al (2014). A database and synthesis of northern peatland soil properties and Holocene carbon and nitrogen accumulation.
Holocene,
24(9), 1028-1042.
Abstract:
A database and synthesis of northern peatland soil properties and Holocene carbon and nitrogen accumulation
Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45°N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 ± 3% (standard deviation) for Sphagnum peat, 51 ± 2% for non-Sphagnum peat, and at 49 ± 2% overall. Dry bulk density averaged 0.12 ± 0.07 g/cm3, organic matter bulk density averaged 0.11 ± 0.05 g/cm3, and total carbon content in peat averaged 47 ± 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 ± 2 (standard error of mean) g C/m2/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25–28 g C/m2/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.
Abstract.
van Geel B, Heijnis H, Charman DJ, Thompson G, Engels S (2014). Bog burst in the eastern Netherlands triggered by the 2.8 kyr BP climate event.
Holocene,
24(11), 1465-1477.
Abstract:
Bog burst in the eastern Netherlands triggered by the 2.8 kyr BP climate event
The nature and cause of the so-called 2.8 kyr BP event have been a subject of much debate. Peat sequences have provided much of the evidence for this event, but the process link between climate and peatland response is not well understood. Multiproxy, high-resolution analysis of a core from Bargerveen in the eastern Netherlands based on pollen, non-pollen palynomorphs, testate amoebae and geochemistry identified an abrupt shift from relatively dry to extremely wet conditions. Radiocarbon-based wiggle-match dating (WMD) and biostratigraphy based on the pollen record show that this shift in local hydrology occurred around 2800 cal. yr BP. We interpret an erosional hiatus lasting up to 950 years immediately prior to this, as the effect of a bog burst after excessive rainfall. This phenomenon was not limited to our sampling location but occurred over a large part of the former Bargerveen. Peat at the hiatus contains microfossils that reflect temporary eutrophication as a consequence of local fires and secondary decomposition because of increased drainage after the erosion event. Our data show how detailed multiproxy analyses can elucidate the past response of peatlands to changing climate and suggest that the climatic change in northwest Europe at this time caused major non-linear disruption to these ecosystems.
Abstract.
Swindles GT, Reczuga M, Lamentowicz M, Raby CL, Turner TE, Charman DJ, Gallego-Sala AV, Valderrama E, Williams C, Draper F, et al (2014). Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function
for Palaeohydrological Reconstruction.
Microbial Ecology: an international journalAbstract:
Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function
for Palaeohydrological Reconstruction
Tropical peatlands represent globally important carbon sinks with a unique biodiversity and are currently threatened by climate change and human activities. It is now imperative that proxy methods are developed to understand the ecohydrological dynamics of these sys- tems and for testing peatland development models. Testate amoebae have been used as environmental indicators in ecological and palaeoecological studies of peatlands, pri- marily in ombrotrophic Sphagnum-dominated peatlands in the mid- and high-latitudes. We present the first ecolog- ical analysis of testate amoebae in a tropical peatland, a nutrient-poor domed bog in western (Peruvian) Amazonia. Litter samples were collected from different hydrological microforms (hummock to pool) along a transect from the edge to the interior of the peatland. We recorded 47 taxa from 21 genera. The most common taxa are Cryptodifflugia oviformis, Euglypha rotunda type, Phryganella acropodia, Pseudodifflugia fulva type and Trinema lineare. One species found only in the southern hemisphere, Argynnia spicata, is present. Arcella spp. Centropyxis aculeata and Lesqueresia spiralis are indicators of pools containing standing water. Canonical correspondence analysis and non-metric multi- dimensional scaling illustrate that water table depth is a significant control on the distribution of testate amoebae, similar to the results from mid- and high-latitudes peat- lands. A transfer function model for water table based on weighted averaging partial least-squares (WAPLS) regres- sion is presented and performs well under cross-validation (r2apparent = 0.76, RMSE = 4.29; r2jack = 0.68, RMSEP = 5.18). The transfer function was applied to a 1-m peat core, and sample-specific reconstruction errors were generated using bootstrapping. The reconstruction generally suggests near-surface water tables over the last 3,000 years, with a shift to drier conditions at c. cal. 1218-1273 AD.
Abstract.
Swindles GT, Reczuga M, Lamentowicz M, Raby CL, Turner TE, Charman DJ, Gallego-Sala A, Valderrama E, Williams C, Draper F, et al (2014). Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function for Palaeohydrological Reconstruction.
Microbial Ecology,
68(2), 284-298.
Abstract:
Ecology of Testate Amoebae in an Amazonian Peatland and Development of a Transfer Function for Palaeohydrological Reconstruction
Tropical peatlands represent globally important carbon sinks with a unique biodiversity and are currently threatened by climate change and human activities. It is now imperative that proxy methods are developed to understand the ecohydrological dynamics of these systems and for testing peatland development models. Testate amoebae have been used as environmental indicators in ecological and palaeoecological studies of peatlands, primarily in ombrotrophic Sphagnum-dominated peatlands in the mid- and high-latitudes. We present the first ecological analysis of testate amoebae in a tropical peatland, a nutrient-poor domed bog in western (Peruvian) Amazonia. Litter samples were collected from different hydrological microforms (hummock to pool) along a transect from the edge to the interior of the peatland. We recorded 47 taxa from 21 genera. The most common taxa are Cryptodifflugia oviformis, Euglypha rotunda type, Phryganella acropodia, Pseudodifflugia fulva type and Trinema lineare. One species found only in the southern hemisphere, Argynnia spicata, is present. Arcella spp. Centropyxis aculeata and Lesqueresia spiralis are indicators of pools containing standing water. Canonical correspondence analysis and non-metric multidimensional scaling illustrate that water table depth is a significant control on the distribution of testate amoebae, similar to the results from mid- and high-latitude peatlands. A transfer function model for water table based on weighted averaging partial least-squares (WAPLS) regression is presented and performs well under cross-validation (rapparent = 0.76, RMSE = 4.29; r2jack = 0.68, RMSEP = 5.18). The transfer function was applied to a 1-m peat core, and sample-specific reconstruction errors were generated using bootstrapping. The reconstruction generally suggests near-surface water tables over the last 3,000 years, with a shift to drier conditions at c. cal. 1218-1273 AD. © 2014 Springer Science+Business Media New York.
Abstract.
Barber KE, Charman DJ (2014). Holocene palaeoclimate records from peatlands.
Global Change in the Holocene, (Eds: John Birks, Rick Battarbee, Anson Mackay, Frank Oldfield),
9780203785027, 210-226.
Abstract:
Holocene palaeoclimate records from peatlands
© 2005 Taylor. &. Francis. All rights reserved. Peat formation is widespread across the globe but the majority of existing proxy climate records come from the ombrotrophic (rain-fed) raised and blanket peat bogs of temperate oceanic regions such as northwest Europe. In North America, peat initiation dates and the spread of peatlands have also been used to infer climate change during the Early to Mid-Holocene. Elsewhere, continuous records of change have been derived from profiles which may span most of the Holocene. Methods focus on the use of biological proxies, ideally used in a multi-proxy approach, to derive continuous bog surface wetness (BSW) curves which are an integrated record of effective precipitation, and on stable isotope measurements which may be directly influenced by temperature and precipitation. Both approaches have been used on recent peats in attempts to validate and calibrate the proxy records against documented climate records with some success, and the results suggest that the impact of summer temperatures on evapotranspiration from bog surfaces is the main factor in changes in BSW in northwest Europe. Within this region, changes in BSW are apparent in many sites at around 8200, 5900, 4400, 3500, 2700, 1700, 1400, 1100, 700 and 250 cal BP. These changes to a cooler/wetter climate are probably caused by circulation changes in the Atlantic Ocean and by solar variability. Ongoing research is providing decadal resolution records of proxy climate which may be used in testing climate models.
Abstract.
Yu Z, Loisel J, Charman DJ, Beilman DW, Camill P (2014). Holocene peatland carbon dynamics in the circum-Arctic region: an introduction.
Holocene,
24(9), 1021-1027.
Abstract:
Holocene peatland carbon dynamics in the circum-Arctic region: an introduction
Peatlands represent the largest and most concentrated carbon pool in the terrestrial biosphere, and their dynamics during the Holocene have had significant impacts on the global carbon cycle. In this Introduction paper, we provide an overview of the contributions presented in this Special Issue on Holocene peatland carbon dynamics. We also provide a brief history and current status of peat-core-based research on peatland carbon dynamics. Finally, we identify and discuss some challenges and opportunities that would guide peatland carbon research in the near future. These challenges and opportunities include the need to fill data gaps and increase geographic representations of peat carbon accumulation records, a better understanding of peatland lateral expansion process and improved estimate of peatland area change over time, developing regional carbon accumulation histories and carbon pool estimates, and projecting and quantifying overall peatland net carbon balance in a changing world.
Abstract.
Charman D (2014). The Holocene. In Catt J, Candy I (Eds.) The History of the Quaternary Research Association, London: the Quaternary Research Association, 377-388.
Jensen BJL, Pyne-O'Donnell S, Plunkett G, Froese DG, Hughes PDM, Sigl M, McConnell JR, Amesbury MJ, Blackwell PG, van den Bogaard C, et al (2014). Transatlantic distribution of the Alaskan White River Ash.
Geology,
42(10), 875-878.
Abstract:
Transatlantic distribution of the Alaskan White River Ash
Volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and/or asynchronous behaviors in Earth system and archaeological sciences. However, it is generally assumed that only exceptionally powerful events, such as supereruptions (≥450 km3 of ejecta as dense-rock equivalent; recurrence interval of ~105 yr), distribute ash broadly enough to have an impact on human society, or allow us to address geologic, climatic, and cultural questions on an intercontinental scale. Here we use geochemical, age, and morphological evidence to show that the Alaskan White River Ash (eastern lobe; A.D. 833-850) correlates to the “AD860B“ ash (A.D. 846-848) found in Greenland and northern Europe. These occurrences represent the distribution of an ash over 7000 km, linking marine, terrestrial, and ice-core records. Our results indicate that tephra from more moderate-size eruptions, with recurrence intervals of ~100 yr, can have substantially greater distributions than previously thought, with direct implications for volcanic dispersal studies, correlation of widely distributed proxy records, and volcanic hazard assessment.
Abstract.
Roland TP, Caseldine CJ, Charman DJ, Turney CSM, Amesbury MJ (2014). Was there a '4.2ka event' in Great Britain and Ireland? Evidence from the peatland record.
Quaternary Science Reviews,
83, 11-27.
Abstract:
Was there a '4.2ka event' in Great Britain and Ireland? Evidence from the peatland record
Palaeoenvironmental and archaeological data from several regions around the world show evidence of a multi-centennial climatic event occurring approximately 4200cal yr BP (4.2ka). Whilst the climatic change and/or impact of the 4.2ka event is clear in certain regions, such as western Asia, evidence for the event has yet to be fully evaluated in northwest Europe. This study presents high-resolution, multi-proxy palaeoclimate records from sites in Northern Ireland, ideally located for an objective examination of the nature of the event in Great Britain and Ireland within the broader context of mid-Holocene climate change c. 6.5-2.5ka. The peatlands of northwest Europe possess considerable potential for the examination of climatic change in the North Atlantic region, demonstrated by the range of palaeohydrological proxy data generated during this study (peat humification, plant macrofossil and testate amoebae analyses) supported by a high-resolution chronology (including comprehensive AMS 14C and tephrochronology). The inter-site testate amoebae reconstructions appear coherent and were combined to produce a regional climatic record, in marked contrast to the plant macrofossil and peat humification records that appear climatically complacent. The testate amoebae reconstruction, however, provides no compelling evidence for a 4.2ka event signal and is consistent with previously reported studies from across northwest Europe, suggesting the origin and impact of this event is spatially complex. © 2013 Elsevier Ltd.
Abstract.
2013
Swindles GT, Lawson IT, Matthews IP, Blaauw M, Daley TJ, Charman DJ, Roland TP, Plunkett G, Schettler G, Gearey BR, et al (2013). Centennial-scale climate change in Ireland during the Holocene.
Earth-Science Reviews,
126, 300-320.
Abstract:
Centennial-scale climate change in Ireland during the Holocene
We examine mid- to late Holocene centennial-scale climate variability in Ireland using proxy data from peatlands, lakes and a speleothem. A high degree of between-record variability is apparent in the proxy data and significant chronological uncertainties are present. However, tephra layers provide a robust tool for correlation and improve the chronological precision of the records. Although we can find no statistically significant coherence in the dataset as a whole, a selection of high-quality peatland water table reconstructions co-vary more than would be expected by chance alone. A locally weighted regression model with bootstrapping can be used to construct a 'best-estimate' palaeoclimatic reconstruction from these datasets. Visual comparison and cross-wavelet analysis of peatland water table compilations from Ireland and Northern Britain show that there are some periods of coherence between these records. Some terrestrial palaeoclimatic changes in Ireland appear to coincide with changes in the North Atlantic thermohaline circulation and solar activity. However, these relationships are inconsistent and may be obscured by chronological uncertainties. We conclude by suggesting an agenda for future Holocene climate research in Ireland. © 2013 Elsevier B.V.
Abstract.
Charman DJ, Beilman DW, Blaauw M, Booth RK, Brewer S, Chambers FM, Christen JA, Gallego-Sala A, Harrison SP, Hughes PDM, et al (2013). Climate-related changes in peatland carbon accumulation during the last millennium.
Biogeosciences,
10(2), 929-944.
Abstract:
Climate-related changes in peatland carbon accumulation during the last millennium
Peatlands are a major terrestrial carbon store and a persistent natural carbon sink during the Holocene, but there is considerable uncertainty over the fate of peatland carbon in a changing climate. It is generally assumed that higher temperatures will increase peat decay, causing a positive feedback to climate warming and contributing to the global positive carbon cycle feedback. Here we use a new extensive database of peat profiles across northern high latitudes to examine spatial and temporal patterns of carbon accumulation over the past millennium. Opposite to expectations, our results indicate a small negative carbon cycle feedback from past changes in the long-term accumulation rates of northern peatlands. Total carbon accumulated over the last 1000 yr is linearly related to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is more important than decomposition in determining long-term carbon accumulation. Furthermore, northern peatland carbon sequestration rate declined over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), probably because of lower LIA temperatures combined with increased cloudiness suppressing net primary productivity. Other factors including changing moisture status, peatland distribution, fire, nitrogen deposition, permafrost thaw and methane emissions will also influence future peatland carbon cycle feedbacks, but our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands in a warmer future. © 2012 Author(s).
Abstract.
Parry LE, Charman DJ, Blake WH (2013). Comparative dating of recent peat deposits using natural and anthropogenic fallout radionuclides and Spheroidal Carbonaceous Particles (SCPs) at a local and landscape scale.
Quaternary Geochronology,
15, 11-19.
Abstract:
Comparative dating of recent peat deposits using natural and anthropogenic fallout radionuclides and Spheroidal Carbonaceous Particles (SCPs) at a local and landscape scale
Proxy records from recently accumulated peats provide valuable information about past environmental change, but they depend on high quality chronological information to calculate rates and timing of change. However, there is uncertainty in the accuracy and consistency of the methodologies used for dating recent peats. This study compares results from Spheroidal Carbonaceous Particles (SCPs) and natural and anthropogenic fallout radionuclides (210Pb, 137Cs and 241Am) used to date three replicate cores from three contrasting sites. Data are used to test the consistency of dating techniques within and between sites, and to assess the impact of local conditions on geochronological results.There is broad consistency in results, but there is also a significant disagreement between dates in a number of cores, both within and between sites. A relatively dry site that had been affected by past burning and erosion showed the greatest consistency between methods and replicate cores. Wetter, less degraded sites showed least consistency. Using patterns of (dis)agreement between dating techniques we assess the potential causes of dating inaccuracy. The data support previous suggestions that 210Pb is mobile in wetter conditions, and suggests that 241Am can be considered an increasingly valuable radionuclide. Finally, our data suggest the current estimates for SCP-based ages in the region maybe incorrect and require further regional calibration.Using several techniques on replicate cores from three sites in the same area has provided a more robust evaluation of the likely reliability of individual techniques and the processes that may adversely affect them. We conclude that until advances are made in understanding the processes behind the variable quality of SCP and fallout radionuclide dating, using two or more dating techniques will greatly improve understanding of the validity of a peatland chronology, especially in wetter locations. © 2013 Elsevier B.V.
Abstract.
Turner TE, Swindles GT, Charman DJ, Blundell A (2013). Comparing regional and supra-regional transfer functions for palaeohydrological reconstruction from Holocene peatlands.
Palaeogeography, Palaeoclimatology, Palaeoecology,
369, 395-408.
Abstract:
Comparing regional and supra-regional transfer functions for palaeohydrological reconstruction from Holocene peatlands
Testate amoebae-based transfer functions are commonly used in peatland palaeoclimate studies. These models have been developed in several regions of the world and are sometimes used for palaeohydrological reconstruction from fossil data in locations where no transfer functions exist. Limitations of this approach may include missing modern analogues and problems associated with site-specific or regional factors in testate amoebae ecology and biogeography. This study presents new testate amoebae-hydrology transfer functions based on data from six peatlands in Northern England. Transfer functions were generated for water table depth and moisture content using weighted averaging tolerance downweighted regression with inverse deshrinking and model performance was assessed using leave-one-out (jacknifing) cross-validation. To examine the robustness of applying transfer functions extra-regionally, we performed a number of spatially independent cross-validation (SICV) tests using contemporary testate amoebae and environmental data from established Northern Ireland and ACCROTELM transfer functions. Inferred water table depths were consistent with observed values in terms of position along the hydrological gradient, however magnitudes varied. We then applied the three independent transfer functions to fossil data from a peatland in Northern England to compare the reconstructions. The results show that the direction of the reconstructions is consistent in terms of wet/dry shifts. However, variation in the magnitudes of the reconstructed water tables is apparent. This probably reflects the sampling regime, including temporal/seasonal effects, and differences in testate amoebae ecology between regions and individual sites. © 2012 Elsevier B.V.
Abstract.
Charman D (2013). Issues and impacts of using computerbased assessments (CBAs) for formative assessment. In (Ed) Computer-assisted Assessment of Students, 85-94.
Parry LE, Charman DJ (2013). Modelling soil organic carbon distribution in blanket peatlands at a landscape scale.
Geoderma,
211-212(1), 75-84.
Abstract:
Modelling soil organic carbon distribution in blanket peatlands at a landscape scale
Blanket peat and other moorland soils store the largest proportion of the soil organic carbon resource (SOC) in the United Kingdom. However, current understanding of the quantity and distribution of upland SOC is limited and approaches are needed to quantify carbon storage over large areas, whilst adequately representing spatial variability at a smaller scale. This article presents a methodology for quantifying and mapping SOC distribution at a landscape scale in blanket peatlands on Dartmoor, South West England. Using stratified sampling, twenty-nine cores were taken from a range of depths within each of the soil types found in the study area. Depth was strongly correlated with bulk density (r2=0.70, P
Abstract.
Royles J, Amesbury MJ, Convey P, Griffiths H, Hodgson DA, Leng MJ, Charman DJ (2013). Plants and soil microbes respond to recent warming on the Antarctic Peninsula.
Curr Biol,
23(17), 1702-1706.
Abstract:
Plants and soil microbes respond to recent warming on the Antarctic Peninsula.
Annual temperatures on the Antarctic Peninsula, one of the most rapidly warming regions on Earth, have risen by up to 0.56°C per decade since the 1950s. Terrestrial and marine organisms have shown changes in populations and distributions over this time, suggesting that the ecology of the Antarctic Peninsula is changing rapidly. However, these biological records are shorter in length than the meteorological data, and observed population changes cannot be securely linked to longer-term trends apparent in paleoclimate data. We developed a unique time series of past moss growth and soil microbial activity from a 150-year-old moss bank at the southern limit of significant plant growth based on accumulation rates, cellulose δ(13)C, and fossil testate amoebae. We show that growth rates and microbial productivity have risen rapidly since the 1960s, consistent with temperature changes, although recently they may have stalled. The recent increase in terrestrial plant growth rates and soil microbial activity are unprecedented in the last 150 years and are consistent with climate change. Future changes in terrestrial biota are likely to track projected temperature increases closely and will fundamentally change the ecology and appearance of the Antarctic Peninsula.
Abstract.
Author URL.
Royles J, Amesbury MJ, Convey P, Griffiths H, Hodgson DA, Leng MJ, Charman DJ (2013). Plants and soil microbes respond to recent warming on the antarctic peninsula.
Current Biology,
23(17), 1702-1706.
Abstract:
Plants and soil microbes respond to recent warming on the antarctic peninsula
Annual temperatures on the Antarctic Peninsula, one of the most rapidly warming regions on Earth, have risen by up to 0.56 C per decade since the 1950s [1]. Terrestrial and marine organisms have shown changes in populations and distributions over this time [2, 3], suggesting that the ecology of the Antarctic Peninsula is changing rapidly. However, these biological records are shorter in length than the meteorological data, and observed population changes cannot be securely linked to longer-term trends apparent in paleoclimate data [4]. We developed a unique time series of past moss growth and soil microbial activity from a 150-year-old moss bank at the southern limit of significant plant growth based on accumulation rates, cellulose δ13C, and fossil testate amoebae. We show that growth rates and microbial productivity have risen rapidly since the 1960s, consistent with temperature changes [5], although recently they may have stalled [2]. The recent increase in terrestrial plant growth rates and soil microbial activity are unprecedented in the last 150 years and are consistent with climate change. Future changes in terrestrial biota are likely to track projected temperature increases closely and will fundamentally change the ecology and appearance of the Antarctic Peninsula. © 2013 Elsevier Ltd.
Abstract.
Amesbury MJ, Mallon G, Charman DJ, Hughes PDM, Booth RK, Daley TJ, Garneau M (2013). Statistical testing of a new testate amoeba-based transfer function for water-table depth reconstruction on ombrotrophic peatlands in north-eastern Canada and Maine, United States.
Journal of Quaternary Science,
28(1), 27-39.
Abstract:
Statistical testing of a new testate amoeba-based transfer function for water-table depth reconstruction on ombrotrophic peatlands in north-eastern Canada and Maine, United States
Proxy reconstructions of climatic parameters developed using transfer functions are central to the testing of many palaeoclimatic hypotheses on Holocene timescales. However, recent work shows that the mathematical models underpinning many existing transfer functions are susceptible to spatial autocorrelation, clustered training set design and the uneven sampling of environmental gradients. This may result in over-optimistic performance statistics or, in extreme cases, a lack of predictive power. A new testate amoeba-based transfer function is presented that fully incorporates the new recommended statistical tests to address these issues. Leave-one-out cross-validation, the most commonly applied method in recent studies to assess model performance, produced over-optimistic performance statistics for all models tested. However, the preferred model, developed using weighted averaging with tolerance downweighting, retained a predictive capacity equivalent to other published models even when less optimistic performance statistics were chosen. Application of the new statistical tests in the development of transfer functions provides a more thorough assessment of performance and greater confidence in reconstructions based on them. Only when the wider research community have sufficient confidence in transfer function-based proxy reconstructions will they be commonly used in data comparison and palaeoclimate modelling studies of broader scientific relevance. © 2012 John Wiley & Sons, Ltd.
Abstract.
Barnett RL, Charman DJ, Gehrels WR, Saher MH, Marshall WA (2013). Testate Amoebae as Sea-level Indicators in Northwestern Norway: Developments in Sample Preparation and Analysis.
ACTA PROTOZOOLOGICA,
52(3), 115-128.
Author URL.
2012
Charman DJ, Hohl V, Blundell A, Mitchell F, Newberry J, Oksanen P (2012). A 1000-year reconstruction of summer precipitation from Ireland: Calibration of a peat-based palaeoclimate record.
Quaternary International,
268, 87-97.
Abstract:
A 1000-year reconstruction of summer precipitation from Ireland: Calibration of a peat-based palaeoclimate record
Calibration of proxy climate records is well-established for annually resolved proxies such as tree rings, but it has not been attempted for non-annually resolved proxies such as those from peatland surface wetness records. Several previous studies have suggested that peatland surface wetness is primarily driven by warm season moisture balance and implied a potential for producing calibrated records of deficit or precipitation. This paper presents a high-resolution testate amoebae analysis of a peat record from central Ireland covering the last c.1000 years, and provides the first attempt to produce a calibrated record of past precipitation from a peat record. Past water table depth was reconstructed using a transfer function applied to contiguous samples for the top 1. m of the profile. The chronology was constrained by a series of radiocarbon ages (including 'bomb-spike' ages) and spheroidal carbonaceous particles. Correlations between reconstructed water tables and meteorological records (1958-1995) of precipitation and deficit were strongly positive and were used to reconstruct precipitation and deficit from the last 1000 years. Validation using earlier meteorological records was hampered by very low peat accumulation rates, but suggested the summer precipitation and deficit reconstructions were more robust than a reconstruction of annual precipitation. The summer precipitation reconstruction suggests that the period AD1400-1850 experienced higher summer rainfall than for much of both the preceding 400 years and the last 150 years. The change in regime from low to high summer rainfall may be attributed to changes in the summer North Atlantic Oscillation. Combined with tree ring and speleothem records of winter NAO, this suggests a major change in seasonality of precipitation in far western Europe between the Medieval Climate Anomaly and the Little Ice Age. The MCA was characterised by dry summers and wet winters, whilst the LIA had wet summers and dry winters. Calibration of peat surface wetness records using meteorological records holds much potential for the future and may lead to improved insights into seasonal precipitation and water balance changes. This study was limited by slow accumulation rates leading to low temporal resolution for the late 19th and early 20th century part of the record. Further development of the technique will require more highly temporally resolved records of change over the whole of the instrumental time period to allow a full calibration and validation approach to be applied. © 2011 Elsevier Ltd and INQUA.
Abstract.
Parry LE, Charman DJ, Noades JPW (2012). A method for modelling peat depth in blanket peatlands.
Soil Use and Management,
28(4), 614-624.
Abstract:
A method for modelling peat depth in blanket peatlands
Inventories of peat volume and carbon storage often include general values for peat depth, but more spatially explicit and accurate estimates are required if carbon management strategies are to be developed at scales appropriate for the management. This article presents a methodology for estimating peat depth for large blanket peat areas using field sampling and GIS modelling to map peat depth on Dartmoor in south-west England. The study area was divided into carbon unit areas (CUAs) based on soil and vegetation. Approximately 1000 peat depth measurements were taken, each consisting of a mean (n=5) from depths within a 32m2 area. Sampling points were stratified according to CUA area and proportional extent of slope and elevation classes. Regression analyses were used to determine the relationships between slope, elevation and peat depth within each CUA. The strongest relationship was for blanket peat (r2=0.53), with weaker ones for areas where peat was shallow and depth was less variable. A digital elevation model was used in a GIS to model peat depths for the whole of Dartmoor. Results were tested against a data set of 200 peat depths on a 250m grid covering 1325ha. We conclude that peat depth can be modelled using easily available topographic data combined with well-designed field sampling over larger spatial scales. The approach can result in accurate mapping of peat depth and carbon storage for blanket peatlands in the United Kingdom and perhaps also elsewhere. © 2012 British Society of Soil Science.
Abstract.
Pyne-O'Donnell SDF, Hughes PDM, Froese DG, Jensen BJL, Kuehn SC, Mallon G, Amesbury MJ, Charman DJ, Daley TJ, Loader NJ, et al (2012). High-precision ultra-distal Holocene tephrochronology in North America.
Quaternary Science Reviews,
52, 6-11.
Abstract:
High-precision ultra-distal Holocene tephrochronology in North America
Far-travelled volcanic ashes (tephras) from Holocene eruptions in Alaska and the Pacific northwest have been traced to the easternmost extent of North America, providing the basis for a new high-precision geochronological framework throughout the continent through tephrochronology (the dating and correlation of tephra isochrons in sedimentary records). The reported isochrons are geochemically distinct, with seven correlated to documented sources in Alaska and the Cascades, including the Mazama ash from Oregon (∼7600 years old) and the eastern lobe of the White River Ash from Alaska (∼1150 years old). These findings mark the beginning of a tephrochronological framework of enhanced precision across North America, with applications in palaeoclimate, surface process and archaeological studies. The particle travel distances involved (up to ∼7000 km) also demonstrate the potential for continent-wide or trans-Atlantic socio-economic disruption from similar future eruptions. © 2012 Elsevier Ltd.
Abstract.
Charman D (2012). Northern peatland carbon accumulation and climate change during the last millennium. Quaternary International, 279
Yu Z, Beilman DW, Frolking S, MacDonald GM, Roulet NT, Camill P, Charman DJ (2012). Peatlands as a model ecosystem of soil carbon dynamics: Reply to Comment on "peatlands and their role in the global carbon cycle". Eos, 93(3).
Väliranta M, Blundell A, Charman DJ, Karofeld E, Korhola A, Sillasoo U, Tuittila ES (2012). Reconstructing peatland water tables using transfer functions for plant macrofossils and testate amoebae: a methodological comparison.
Quaternary International,
268, 34-43.
Abstract:
Reconstructing peatland water tables using transfer functions for plant macrofossils and testate amoebae: a methodological comparison
Relatively seldom is the same parameter reconstructed from the same site using different proxies, resulting in a persistent problem for palaeoecological studies whereby a reconstruction based on a single-proxy may provide an unequivocal view of the changes in past conditions. Plant macrofossils and testate amoebae are commonly used proxies to reconstruct past changes in peatland surface moisture conditions, but there are no comparisons between quantitative reconstructions based on both techniques. This paper compares two high-resolution late-Holocene quantitative water table (WT) reconstructions based on transfer functions for plant macrofossils and testate amoebae from two boreal peatland sites in Finland and Estonia. The reconstructed WT variation patterns during the last ca. 5000 years are almost identical in directions for both proxies. However, both bog records contain one inconsistent episode when the two proxies indicate different hydrological conditions. In both cases, the testate amoebae reconstruction shows wetter than the average conditions, whereas the plant-based reconstruction indicates drier than the average conditions. Several, possibly simultaneously affecting, reasons can be suggested for mismatches between proxies: 1) the proxies have different response times and sensitivities to hydrological changes, 2) the species-ecology is inadequately known, 3) the modern analogues are poor, 4) the microhabitat dynamics are unpredictable, and 5) the modern data set is too small. Divergences between the proxy records emphasize the fact that single-proxy reconstructions are subject to larger uncertainties than those based on two or more methods. © 2011 Elsevier Ltd and INQUA.
Abstract.
Payne RJ, Telford RJ, Blackford JJ, Blundell A, Booth RK, Charman DJ, Lamentowicz Ł, Lamentowicz M, Mitchell EAD, Potts G, et al (2012). Testing peatland testate amoeba transfer functions: Appropriate methods for clustered training-sets.
Holocene,
22(7), 819-825.
Abstract:
Testing peatland testate amoeba transfer functions: Appropriate methods for clustered training-sets
Transfer functions are widely used in palaeoecology to infer past environmental conditions from fossil remains of many groups of organisms. In contrast to traditional training-set design with one observation per site, some training-sets, including those for peatland testate amoeba-hydrology transfer functions, have a clustered structure with many observations from each site. Here we show that this clustered design causes standard performance statistics to be overly optimistic. Model performance when applied to independent data sets is considerably weaker than suggested by statistical cross-validation. We discuss the reasons for these problems and describe leave-one-site-out cross-validation and the cluster bootstrap as appropriate methods for clustered training-sets. Using these methods we show that the performance of most testate amoeba-hydrology transfer functions is worse than previously assumed and reconstructions are more uncertain. © the Author(s) 2011.
Abstract.
Hughes PDM, Mallon G, Essex HJ, Amesbury MJ, Charman DJ, Blundell A, Chambers FM, Daley TJ, Mauquoy D (2012). The use of k-values to examine plant 'species signals' in a peat humification record from Newfoundland.
Quaternary International,
268, 156-165.
Abstract:
The use of k-values to examine plant 'species signals' in a peat humification record from Newfoundland
Peat humification analysis has been used widely over the last three decades to reconstruct bog surface wetness (BSW) for use as a palaeoclimate proxy. The technique has the advantage that it is quick and relatively inexpensive to perform, allowing for high resolution and contiguous sampling of peat archives. However, some concerns have been raised over the quality of the resultant proxy-climate records because changes in the plant species composition of peat may contribute a 'species signal' to records, potentially confusing the relationship between bog water table position and the apparent degree of peat humification. This paper uses the k-values of fresh plant material (sensu Overbeck, 1947 - i.e. the absorption value of the alkali extracts of fresh plant material) to explore the impact of changing plant colouration in a Holocene peat humification-based palaeoclimate archive from Newfoundland. We calculate k-scores for peat samples, using plant macrofossil data and the k-values of individual species to provide a down-core visualisation of the plant species signal. Although, overall, the humification data are validated, comparison of the original humification data with a k-adjusted version shows that the species signal is sometimes sufficient to change the timing and number of decadal to centennial-scale events recorded in the data as well as millennial to multi-millennial-scale trends. © 2011.
Abstract.
2011
Niinemets E, Pensa M, Charman DJ (2011). Analysis of fossil testate amoebae in Selisoo Bog, Estonia: Local variability and implications for palaeoecological reconstructions in peatlands.
Boreas,
40(2), 367-378.
Abstract:
Analysis of fossil testate amoebae in Selisoo Bog, Estonia: Local variability and implications for palaeoecological reconstructions in peatlands
Local variability in decadal water-table changes on an ombrotrophic peatland was explored using testate amoebae analysis of near-surface peats in an Estonian raised bog. The distribution of testate amoebae assemblages was studied along the gradient from hummock to hollow in the upper 30-cm layer of peat. As expected, testate amoebae assemblages in different micro-ecotypes from hummock to hollow, even as close as 10m apart, are distinctly different. Past water-table change was reconstructed by applying a transfer function based on modern samples from throughout Europe. Results show a decline in water level from the mid-late 20th century on Selisoo bog in all profiles from the different micro-ecotypes. However, the absolute water-table depths and amplitudes of fluctuations vary between reconstructions from different sampling micro-ecotypes. Cores were correlated using changes in non-mire pollen concentrations down-core, but it was not possible to correlate minor changes in water-table owing to non-contiguous sampling and variable accumulation rates. We conclude that different microtopes show the same decadal trends in relative water-table change but that the absolute magnitude of change may be more variable locally. It is important that reconstructed palaeohydrological changes in bogs consider changes in bog micro-ecotypes, and their variation over time, as this may alter the sensitivity of an individual record to drivers such as climate change. Comparison and compilation of data from parallel cores from different micro-ecotypes and/or different sites are likely to provide more robust reconstructions. © 2010 the Authors. Boreas © 2010 the Boreas Collegium.
Abstract.
Pancost RD, McClymont EL, Bingham EM, Roberts Z, Charman DJ, Hornibrook ERC, Blundell A, Chambers FM, Lim KLH, Evershed RP, et al (2011). Archaeol as a methanogen biomarker in ombrotrophic bogs.
Organic Geochemistry,
42(10), 1279-1287.
Abstract:
Archaeol as a methanogen biomarker in ombrotrophic bogs
In order to develop new tools in the reconstruction of microbiological processes in ancient continental settings, we determined the concentration of archaeol and sn-2-hydroxyarchaeol in four Holocene ombrotrophic peatlands, spanning a range of European climate zones. Neither ether lipid was present in the aerobic acrotelm peat, consistent with an origin from anaerobic archaea, presumably methanogens. At the depth of the maximum seasonal water table, archaeol and sn-2-hydroxyarchaeol concentration markedly increased at all four sites, again consistent with an anaerobic source, but differed strongly among sites. The differences apparently reflect a combination of vegetation - ericaceous and graminoid plants as opposed to Sphagnum spp. and other mosses lacking root systems - and temperature influence on methanogenesis. In particular, low ether lipid concentrations in Finland probably reflect the lack of vascular vegetation possessing well-developed root systems, together with low mean annual temperature. Similarly low concentrations of archaeol and sn-2-hydroxyarchaeol in a German bog likely result from winter temperatures below 0. °C and a relatively shorter growing season. The occurrence of sn-2-hydroxyarchaeol is limited to a narrow and shallow depth range, indicating that it is poorly preserved, but archaeol persists throughout the cores. Decoupling the concentration of archaeol and the more labile sn-2-hydroxyarchaeol below ca. 50 cm suggests that the former records fossil biomass rather than living biomass. If so, then downcore variation in archaeol concentration likely reflects past changes in methane cycling, and archaeol, pending further developmental research, could serve as a new tool for reconstruction of past peatland biogeochemistry. © 2011 Elsevier Ltd.
Abstract.
Yu Z, Beilman DW, Frolking S, MacDonald GM, Roulet NT, Camill P, Charman DJ (2011). Peatlands and their role in the global carbon cycle.
Eos,
92(12), 97-98.
Abstract:
Peatlands and their role in the global carbon cycle
Global peatlands store a very large carbon (C) pool located within a few meters of the atmosphere. Thus, peatland-atmosphere C exchange should be a major concern to global change scientists: Will large amounts of respired belowground C be released in a warmer climate, causing the climate to further warm (a positive climate feedback)? Will more C be sequestered due to increased plant growth in a warmer climate? How will land use change, fires, and permafrost thaw affect the magnitude and direction of carbon dioxide (CO2) and methane (CH4) exchange with the atmosphere? These questions remain challenging, but some significant progress has been made recently.
Abstract.
2010
Kelly A, Charman DJ, Newnham RM (2010). A last glacial maximum pollen record from bodmin moor showing a possible cryptic Northern refugium in Southwest England.
Journal of Quaternary Science,
25(3), 296-308.
Abstract:
A last glacial maximum pollen record from bodmin moor showing a possible cryptic Northern refugium in Southwest England
A late Devensian palynological record is presented from Dozmary Pool (Bodmin Moor, southwest England), beyond the southern limit of the Last Glacial Maximum (LGM) British Ice Sheet. The pollen assemblages indicate predominantly herbaceous tundra-steppe communities but also include elevated levels (typically 10-20%) of conifer tree pollen (Picea, Pinus, Abies) and lower but persistent percentages of broadleaf tree pollen during the LGM. This record is seemingly at odds with the orthodox view of an entirely treeless tundra-steppe environment for this region and elimination of tree species from the British Isles during glacial maxima. Long-distance pollen transport seems an unlikely explanation for the tree pollen considering distance to the nearest known refugia, except possibly for Pinus. Reworking of the tree pollen, often invoked in these circumstances, remains a possible alternative, especially given the abundance of these trees in the region during early Devensian interstadials. However, this explanation has been challenged by studies reporting plant macrofossil and faunal evidence for survival of temperate biota during glacial maxima and from climate modelling work that suggests some trees could have survived the glacial extremes in areas well beyond the recorded glacial refugia. Assuming reworking was not a major factor, the Dozmary Pool pollen record is consistent with the 'cryptic northern refugia hypothesis' that invokes survival of trees in small, scattered populations under locally favourable conditions during glacial maxima. © 2009 John Wiley & Sons, Ltd.
Abstract.
Billett MF, Charman DJ, Clark JM, Evans CD, Evans MG, Ostle NJ, Worrall F, Burden A, Dinsmore KJ, Jones T, et al (2010). Carbon balance of UK peatlands: Current state of knowledge and future research challenges.
Climate Research,
45(1), 13-29.
Abstract:
Carbon balance of UK peatlands: Current state of knowledge and future research challenges
The retention of peatland carbon (C) and the ability to continue to draw down and store C from the atmosphere is not only important for the UK terrestrial carbon inventory, but also for a range of ecosystem services, the landscape value and the ecology and hydrology of ∼15% of the land area of the UK. Here we review the current state of knowledge on the C balance of UK peatlands using several studies which highlight not only the importance of making good flux measurements, but also the spatial and temporal variability of different flux terms that characterise a landscape affected by a range of natural and anthropogenic processes and threats. Our data emphasise the importance of measuring (or accurately estimating) all components of the peatland C budget. We highlight the role of the aquatic pathway and suggest that fluxes are higher than previously thought. We also compare the contemporary C balance of several UK peatlands with historical rates of C accumulation measured using peat cores, thus providing a long-term context for present-day measurements and their natural year-on-year variability. Contemporary measurements from 2 sites suggest that current accumulation rates (-56 to -72 g C m-2 yr-1) are at the lower end of those seen over the last 150 yr in peat cores (-35 to -209 g C m-2 yr-1). Finally, we highlight significant current gaps in knowledge and identify where levels of uncertainty are high, as well as emphasise the research challenges that need to be addressed if we are to improve the measurement and prediction of change in the peatland C balance over future decades. © Inter-Research 2010.
Abstract.
Charman DJ (2010). Centennial climate variability in the British Isles during the mid-late Holocene.
Quaternary Science Reviews,
29(13-14), 1539-1554.
Abstract:
Centennial climate variability in the British Isles during the mid-late Holocene
Multi-millennial climate changes were relatively minor over the mid-late Holocene in the British Isles, because orbitally forced insolation changes were smaller than those at higher latitudes. Centennial climate variability is thus likely to have exerted a greater influence on the environment and human society of the region. Proxy-climate records from the British Isles covering the last 4500years are assembled and re-evaluated with the aim of identifying centennial climate variability reflected by multi-proxy indicators. The proxies include bog oak populations, peatland surface wetness, flooding episodes from fluvial deposits, speleothem annual band width and oxygen isotopes, chironomids from lake sediments and sand and dune deposition. Most proxies reflect water balance rather than temperature alone, and records predominantly reflect warm season climate. A series of 12 key periods of enhanced precipitation-evaporation (P-E) are identified by their presence in two or more proxy records. Variability in P-E is much greater than that shown by temperature proxies and there is no necessary association between warm/cool and dry/wet periods. Although the data for temperature are less robust than those for P-E, a series of key temperature changes are proposed based on speleothem δ18O and chironomid inferred July temperature records; relatively cool before c. 3100years BP, warmer (3100-2000years BP), cool (2000-1250cal years BP), warm (1250-650cal years BP), and cool (650cal years BP onwards). Some key increases in P-E (2750, 1650, 550cal years BP) show a strong correspondence with 'Bond cycles' in ocean proxy records for increased ice rafted debris, decreased summer sea surface temperatures and sometimes decreased North Atlantic deep water circulation. Other higher frequency changes in P-E are also strongly related to SST variability. Whilst some of the main changes to cooler SSTs and increased P-E are approximately coincident with reduced solar output, most are not and thus must be the result of the internal dynamics of the ocean and atmosphere. Future work should concentrate on firmly establishing the pattern of temperature change, improving chronological accuracy and precision in existing records and improving process-based understanding of proxies. © 2009 Elsevier Ltd.
Abstract.
Charman DJ, McCarroll D (2010). Climate variability of the British Isles and adjoining seas. Quaternary Science Reviews, 29(13-14), 1503-1506.
Charman DJ, McCarroll D, Eds (2010). Climate variability of the British Isles and adjoining seas.
Kelly A, Charman DJ, Newnham RM (2010). Comment: a Last Glacial Maximum pollen record from Bodmin Moor showing a possible cryptic northern refugium in southwest England Reply.
JOURNAL OF QUATERNARY SCIENCE,
25(5), 828-829.
Author URL.
Booth RK, Lamentowicz M, Charman DJ (2010). Preparation and analysis of testate amoebae in peatland palaeoenvironmental studies. Mires and Peat, 7, 1-7.
Charman DJ, Gehrels WR, Manning C, Sharma C (2010). Reconstruction of recent sea-level change using testate amoebae.
Quaternary Research,
73(2), 208-219.
Abstract:
Reconstruction of recent sea-level change using testate amoebae
Proxy-based sea-level reconstructions place the instrumentally observed rates of recent sea-level rise in a longer term context by providing data that extend the instrumental sea-level record into past centuries. This paper presents the first sea-level reconstructions based on analyses of testate amoebae, to test their ability to produce high-precision reconstructions of past sea level. We present two reconstructions for the past 100 yr from sites in Maine (USA) and Nova Scotia (Canada) based on short cores from salt marshes, and modern training data from North America and the United Kingdom. These are compared with tide-gauge records and reconstructions based on foraminifera from the same cores. The reconstructions show good agreement with both the tide-gauge data and the foraminifera-based reconstructions. The UK data perform well in predicting known elevations of North American surface samples and produce sea-level reconstructions very similar to those based on the North American data, suggesting the methodology is robust across large geographical areas. We conclude that testate amoebae have the potential to provide robust, higher precision sea-level reconstructions for the past few centuries if modern transfer functions are improved and core sites are located within the main zone of testate amoebae occurrence on the salt marsh. © 2009 University of Washington.
Abstract.
Kelly A, Charman DJ, Newnham RM (2010). Reply to Comment: a Last Glacial Maximum pollen record from Bodmin Moor showing a possible cryptic northern refugium in southwest England. (Kelly et al. 2010). Journal of Quaternary Science, 25(5), 828-829.
Payne R, Gauci V, Charman DJ (2010). The impact of simulated sulfate deposition on peatland testate amoebae.
Microb Ecol,
59(1), 76-83.
Abstract:
The impact of simulated sulfate deposition on peatland testate amoebae.
Peatlands subjected to sulfate deposition have been shown to produce less methane, believed to be due to competitive exclusion of methanogenic archaea by sulfate-reducing bacteria. Here, we address whether sulfate deposition produces impacts on a higher microbial group, the testate amoebae. Sodium sulfate was applied to experimental plots on a Scottish peatland and samples extracted after a period of more than 10 years. Impacts on testate amoebae were tested using redundancy analysis and Mann-Whitney tests. Results showed statistically significant impacts on amoebae communities particularly noted by decreased abundance of Trinema lineare, Corythion dubium, and Euglypha rotunda. As the species most reduced in abundance are all small bacterivores we suggest that our results support the hypothesis of a shift in dominant prokaryotes, although other explanations are possible. Our results demonstrate the sensitivity of peatland microbial communities to sulfate deposition and suggest sulfate may be a potentially important secondary control on testate amoebae communities.
Abstract.
Author URL.
2009
Plunkett G, Whitehouse NJ, Hall VA, Charman DJ, Blaauw M, Kelly E, Mulhall I (2009). A multi-proxy palaeoenvironmental investigation of the findspot of an Iron Age bog body from Oldcroghan, Co. Offaly, Ireland.
Journal of Archaeological Science,
36(2), 265-277.
Abstract:
A multi-proxy palaeoenvironmental investigation of the findspot of an Iron Age bog body from Oldcroghan, Co. Offaly, Ireland
In 2003, the remains of an Early Iron Age bog body, known as 'Oldcroghan Man', were recovered during the cutting of a drainage ditch in a bog in the Irish Midlands. Only some fingernails and a withe fragment remained undisturbed in situ in the drain face, providing the sole evidence for the original position of the body. A detailed reconstruction of the depositional context of the body has been undertaken through multi-proxy analyses of a peat monolith collected at the findspot. The palynological record shows that the surrounding area was the focus of intensive human activity during the Later Bronze Age, but was largely abandoned during the Bronze Age-Iron transition in the mid-first millennium BC. In the mid-4th century BC, a bog pool developed at the site, evidenced in the stratigraphic, plant macrofossil, testate amoebae and coleopteran records. Plant macrofossil and pollen analysis of peat samples associated with the fingernails suggests that the body was deposited in this pool most likely during the 3rd century BC. The absence of carrion beetle fauna points to complete submergence of the body within the pool. Deposition occurred shortly before or around the time that the surrounding area again became the focus of woodland clearance, as seen in the extended pollen record from the peat monolith. This period corresponds to the Early Iron Age in Ireland, during which renewed cultural connections with Britain and continental Europe can be seen in the archaeological record and widespread forest clearance is recorded in pollen records from across Ireland. The palaeoenvironmental results indicate, therefore, that the demise of Oldcroghan Man took place at a pivotal time of socio-economic and perhaps political change. © 2008 Elsevier Ltd. All rights reserved.
Abstract.
Charman DJ, Barber KE, Blaauw M, Langdon PG, Mauquoy D, Daley TJ, Hughes PDM, Karofeld E (2009). Climate drivers for peatland palaeoclimate records.
Quaternary Science Reviews,
28(19-20), 1811-1819.
Abstract:
Climate drivers for peatland palaeoclimate records
Reconstruction of hydroclimate variability is an important part of understanding natural climate change on decadal to millennial timescales. Peatland records reconstruct 'bog surface wetness' (BSW) changes, but it is unclear whether it is a relative dominance of precipitation or temperature that has driven these variations over Holocene timescales. Previously, correlations with instrumental climate data implied that precipitation is the dominant control. However, a recent chironomid inferred July temperature record suggested temperature changes were synchronous with BSW over the mid-late Holocene. This paper provides new analyses of these data to test competing hypotheses of climate controls on bog surface wetness and discusses some of the distal drivers of large-scale spatial patterns of BSW change. Using statistically based estimates of uncertainty in chronologies and proxy records, we show a correlation between Holocene summer temperature and BSW is plausible, but that chronologies are insufficiently precise to demonstrate this conclusively. Simulated summer moisture deficit changes for the last 6000 years forced by temperature alone are relatively small compared with observations over the 20th century. Instrumental records show that summer moisture deficit provides the best explanatory variable for measured water table changes and is more strongly correlated with precipitation than with temperature in both Estonia and the UK. We conclude that BSW is driven primarily by precipitation, reinforced by temperature, which is negatively correlated with precipitation and therefore usually forces summer moisture deficit in the same direction. In western Europe, BSW records are likely to be forced by changes in the strength and location of westerlies, linked to large-scale North Atlantic ocean and atmospheric circulation. © 2009 Elsevier Ltd. All rights reserved.
Abstract.
Swindles GT, Charman DJ, Roe HM, Sansum PA (2009). Environmental controls on peatland testate amoebae (Protozoa: Rhizopoda) in the North of Ireland: Implications for Holocene palaeoclimate studies.
Journal of Paleolimnology,
42(1), 123-140.
Abstract:
Environmental controls on peatland testate amoebae (Protozoa: Rhizopoda) in the North of Ireland: Implications for Holocene palaeoclimate studies
The environmental controls on modern peatland testate amoebae (Protozoa: Rhizopoda) in the North of Ireland were investigated to assess the potential for Holocene palaeoclimate research within this region. Canonical Correspondence Analysis (CCA) revealed that hydrological factors (water table depth and moisture content) are the most important abiotic controls on organism distribution. A series of partial CCAs showed that water table depth explains 15. 8% and moisture content explains 5. 5% of the total variance. Monte-Carlo permutation tests showed that the results are highly significant (p < 0. 002; p < 0. 040 respectively). Transfer functions were generated for water table depth using weighted averaging tolerance downweighted (WA-Tol) regression and for moisture content using weighted averaging partial least squares regression (WA-PLS). The performance of the models was assessed using leave-one-out cross-validation (jacknifing). After removal of outlier samples, the improved transfer functions were found to perform well with an r2jack and root mean square error of predictionjack of 0. 83, 4. 99 cm for water table depth and 0. 76, 4. 60% for moisture content respectively. The water table transfer function was applied to a fossil peat sequence from this region and reconstruction errors were generated by 1,000 bootstrap cycles. The water table reconstruction was also carried out using an established pan-European transfer function and was found to be similar to that based on the North of Ireland dataset. This demonstrates the persistent and comparable control of hydrological variables on the distribution of testate amoebae taxa across Europe and implies that regional training sets can suffice as long as no-analogue situations are not encountered. © 2008 Springer Science+Business Media B.V.
Abstract.
Charman SD, Gregory AH, Carlucci M (2009). Exploring the Diagnostic Utility of Facial Composites: Beliefs of Guilt can Bias Perceived Similarity Between Composite and Suspect.
Journal of Experimental Psychology: Applied,
15(1), 76-90.
Abstract:
Exploring the Diagnostic Utility of Facial Composites: Beliefs of Guilt can Bias Perceived Similarity Between Composite and Suspect
Facial composite research has generally focused on the investigative utility of composites-using composites to find suspects. However, almost no work has examined the diagnostic utility of facial composites-the extent to which composites can be used as evidence against a suspect. For example, detectives and jurors may use the perceived similarity of a suspect to a composite as evidence to determine the likelihood of a suspect's guilt. However, research in social cognition and models of cognitive coherence suggest that these similarity judgments may be biased by evaluators' preexisting beliefs of guilt. Two studies examined how preexisting beliefs of guilt influence similarity ratings between a suspect and a facial composite. Study 1 (n = 93) demonstrated that mock-investigators' beliefs in a suspect's guilt inflated their subsequent similarity ratings. Study 2 (n = 49) demonstrated that mock-jurors' beliefs in a defendant's guilt predicted their similarity ratings. These findings highlight a problem of using facial composites as evidence against a suspect, and demonstrate the malleability of similarity judgments. © 2009 American Psychological Association.
Abstract.
Charman DJ (2009). Peat and Peatlands. In Likens GE (Ed) Encyclopedia of Inland Waters, Oxford: Elsevier, 541-548.
McClymont EL, Mauquoy D, Yeloff D, Broekens P, van Geel B, Charman DJ, Pancost RD, Chambers FM, Evershed RP (2009). The disappearance of Sphagnum imbricatum from Butterburn Flow, UK: a reply to comments by Bjorn Robroek et al.
Holocene,
19(7), 1094-1097.
Abstract:
The disappearance of Sphagnum imbricatum from Butterburn Flow, UK: a reply to comments by Bjorn Robroek et al.
We welcome the comments by Bjorn Robroek et al. (The Holocene 19 (2009) 1093-1094, this issue) on our paper (McClymont et al. the Holocene 18 (2008) 991-1002) and the opportunity to discuss further the complexities that surround the disappearance of Sphagnum imbricatum from Butterburn Flow (our study), and the implications for understanding the disappearance of this species in northwest Europe. We also wish to clarify our site of study; we presented data only from Butterburn Flow, northern England. Although we note that the disappearance of S. imbricatum here is part of a wider European decline in the late Holocene, we did not present data from Wales or Ireland as suggested in the opening paragraph of Robroek's comment. We also noted that the replacement of S. imbricatum by S. magellanicum occurred over c. 44 years, but proposed that it may have been longer owing to evidence for reduced peat accumulation across the transition.
Abstract.
Bingham EM, McClymont EL, Childs EV, Pancost RD, Charman D, Evershed RP (2009). The stanol: Delta(5)-sterol ratio as a proxy for palaeoredox conditions in mires.
Author URL.
2008
Parish F, Sirin A, Charman D, Joosten H, Minayeva T, Silvius M, Stringer L, Eds (2008). Assessment on peatlands, biodiversity and climate change: Main Report. Kuala Lumpur and Wageningen, Global Environment Centre. and Wetlands International.
Amesbury MJ, Charman DJ, Fyfe RM, Langdon PG, West S (2008). Bronze Age upland settlement decline in southwest England: testing the climate change hypothesis.
Journal of Archaeological Science,
35(1), 87-98.
Abstract:
Bronze Age upland settlement decline in southwest England: testing the climate change hypothesis
The division of land on Dartmoor during the Bronze Age by the construction of moor-wide boundaries known as reaves represents a significant development in agricultural practice and land tenure. Previous research relating to the Dartmoor reaves suggests this way of life may have continued for no longer than 200-400 years. It has been suggested that their abandonment occurred as the result of a deteriorating climate, although there are no published palaeoclimatic reconstructions from the area. We therefore test the hypothesis that on Dartmoor, a marked climatic deterioration occurred in the late Bronze Age that can be linked to the abandonment of the reaves. A palaeoclimatic reconstruction derived from testate amoebae and peat humification analyses is presented from Tor Royal Bog, central Dartmoor, the first such record from southwest England. A major shift to a cooler and/or wetter climate is inferred from ca. 1395 to 1155 cal BC that is coincident with the period hypothesised as encompassing the abandonment. This climatic deterioration is replicated in sites in northern Britain, suggesting it was a widespread event. It is concluded that while the evidence supports a climatically forced retreat, there are a range of other socio-economic factors that must also be taken into consideration. © 2007 Elsevier Ltd. All rights reserved.
Abstract.
van der Linden M, Vickery E, Charman DJ, van Geel B (2008). Effects of human impact and climate change during the last 350 years recorded in a Swedish raised bog deposit.
Palaeogeography, Palaeoclimatology, Palaeoecology,
262(1-2), 1-31.
Abstract:
Effects of human impact and climate change during the last 350 years recorded in a Swedish raised bog deposit
A peat core from an ombrotrophic mire in central Sweden was analysed for multi-proxy indicators (plant macrofossils, pollen/non-pollen microfossils, testate amoebae, colorimetric humification, carbon/nitrogen ratios, bulk densities, loss on ignition), to evaluate the relative contributions of climate change and human impact on vegetation and peat accumulation during the last c. 350 years. 14C wiggle-match dating was applied for high precision dating. Testate amoebae assemblages were used to reconstruct past water table depths and compared with other proxies and instrumental climate data from the mid-18th century onwards. Changes in mire surface wetness were mainly caused by climate change (precipitation and evaporation), but the internal dynamics of the local bog vegetation may also have played a role in the recorded water table changes. The human impact signal in the pollen data was compared with Swedish population and land-use data. A link between climate change, human impact (openness of the vegetation) and demographic change was found. Cold and wet periods show a decrease in human impact and open land indicators in the pollen data, followed by an increase in death rate and/or an increase in emigration. © 2008 Elsevier B.V. All rights reserved.
Abstract.
Charman DJ, Minayeva T, Laine J, Sirin A (2008). Impacts of future climate change on peatlands. In Parish F, Sirin A, Charman D, Joosten J, Minayeva T, Silvius M, Stringer L (Eds.) Assessment on peatlands, biodiversity and climate change, Kuala Lumpur and Wageningen: Global Environment Centre and Wetlands International, 139-154.
van der Linden M, Barke J, Vickery E, Charman DJ, van Geel B (2008). Late Holocene human impact and climate change recorded in a North Swedish peat deposit.
Palaeogeography, Palaeoclimatology, Palaeoecology,
258(1-2), 1-27.
Abstract:
Late Holocene human impact and climate change recorded in a North Swedish peat deposit
A peat core from a mire with poor fen lawns and ombrotrophic hummock strings in Northern Sweden was examined (plant macrofossils, pollen/non-pollen microfossils, testate amoebae, colorimetric humification, carbon/nitrogen ratios, bulk densities, loss on ignition) to investigate the effects of climate change and human impact on the plant species composition and peat accumulation of the peat forming vegetation during the last 1700 yr. 14C wiggle-match dating was applied for high-precision dating. The Lappmyran region was dominated by Pinus and Picea forest. Changes in land-use patterns and population density were visible in the pollen record of the regional vegetation. Juniperus and Rumex acetosa-type pollen indicated the presence of grazed land in the area between AD 1500 and 1950. The vegetation at the coring spot gradually became ombrotrophic. The local plant and testate amoebae compositions reflect changes in surface wetness caused by changes in precipitation and the internal dynamics of the bog. A wet interval was observed during the Maunder minimum of solar activity. The presence of Drepanocladus fluitans indicates less ombrotrophic conditions during this period probably caused by the inflow of minerogenic water from upslope owing to increased precipitation. The reconstructed water table shows agreement with precipitation measurements which were available since AD 1860. © 2007 Elsevier B.V. All rights reserved.
Abstract.
Verschuren D, Charman DJ (2008). Latitudinal linkages in late-Holocene moisture-balance variation. In Battarbee RW, Binney HA (Eds.) Natural climate variability and global warming, Blackwell Pub, 189-231.
Blundell A, Charman DJ, Barber K (2008). Multiproxy late Holocene peat records from Ireland: Towards a regional palaeoclimate curve.
Journal of Quaternary Science,
23(1), 59-71.
Abstract:
Multiproxy late Holocene peat records from Ireland: Towards a regional palaeoclimate curve
Two new peat-based climate records from Ireland covering the late Holocene are presented. The sequences are dated by a strong chronological framework formed by AMS radiocarbon dates and SCPs. Three proxy indicators (testate amoebae, macrofossils and humification) have been determined allowing the limitations and strengths of each to be identified and utilised to provide a bog surface wetness (BSW) record for both sites. Age-depth models take into account the potential for accumulation rates to vary with bog vegetation. The records from each site have been used to derive a combined BSW record that displays changes to a wetter/cooler climate from ca. AD 30 (1920 BP), ca. AD 310 (1640 BP), ca. AD 805 (1145 BP), ca. AD 1040 (910 BP) and ca. AD 1300 (650 BP). Changes follow closely those identified in a northern Britain composite BSW record and largely correspond with lake-level data in central France suggesting the main changes in water balance were coherent over a large region. Correspondence with increases in IRD and slower Iceland-Scotland Overflow Water (ISOW) suggests that these changes were related to oceanic forcing influencing the track of dominant westerly air flow over Ireland. Copyright © 2007 John Wiley & Sons, Ltd.
Abstract.
Charman DJ (2008). Peatlands and environmental change: a long term perspective on peatland management and restoration. Thorne and Hatfield Moors Papers, 7, 31-38.
Charman DJ, Booth RK, Makila M, Sirin A (2008). Peatlands and past climate change. In Parish F, Sirin A, Charman D, Joosten H, Minayeva T, Silvius M, Stringer L (Eds.) Assessment on peatlands, biodiversity and climate change, Kuala Lumpur and Wageningen: Global Environment Centre and Wetlands International, 39-59.
Massey AC, Gehrels WR, Charman DJ, Milne GA, Peltier WR, Lambeck K, Selby KA (2008). Relative sea-level change and postglacial isostatic adjustment along the coast of south Devon, United Kingdom.
Journal of Quaternary Science,
23(5), 415-433.
Abstract:
Relative sea-level change and postglacial isostatic adjustment along the coast of south Devon, United Kingdom
Previous sea-level studies suggest that southwest Britain has the fastest subsiding coastline in the United Kingdom, but tide-gauge data, GPS and gravity measurements and geophysical models show little evidence of anomalous subsidence in this region. In this paper we present 15 new sea-level index points from four coastal barrier systems in south Devon. Eight are from compaction-free basal sediments and others were corrected for autocompaction. Our data suggest that relative sea level along the south Devon coastline has risen by 21 ± 4 m during the past 9000 years. Sea-level rise slowed during the middle and late Holocene and a rise of 8 ± 1 m has occurred since ca. 7000 cal. yr BP. Anomalous ages for many rejected points are attributed to sediment reworking during barrier transgression. The relative sea-level history during the early and middle Holocene shows a good fit with geophysical model predictions, but the geological and modelled data diverge in the later Holocene. Unlike the geophysical models, sea-level index points cannot differentiate between late Holocene relative sea-level histories of south Devon and southwest Cornwall. It is suggested that this discrepancy can be resolved by obtaining additional high-quality sea-level index points covering the past 4000 years. Copyright © 2008 John Wiley & Sons, Ltd.
Abstract.
Mitchell EAD, Charman DJ, Warner BG (2008). Testate amoebae analysis in ecological and paleoecological studies of wetlands: Past, present and future.
Abstract:
Testate amoebae analysis in ecological and paleoecological studies of wetlands: Past, present and future
Abstract.
Payne RJ, Charman DJ, Matthews S, Eastwood WJ (2008). Testate amoebae as palaeohydrological proxies in Sürmene Aǧaçbaşi Yaylasi Peatland (Northeast Turkey).
Wetlands,
28(2), 311-323.
Abstract:
Testate amoebae as palaeohydrological proxies in Sürmene Aǧaçbaşi Yaylasi Peatland (Northeast Turkey)
Testate amoebae are unicellular micro-organisms whose hydrological sensitivity and good preservation in peats make them valuable proxies for past peatland surface wetness, and therefore climate. Previous testate amoebae transfer functions have been spatially restricted with no studies from Asia. To derive a transfer function, a sequence of samples was extracted from an ombrotrophic peatland in Turkey and amoebae counted. The internal structure of the data was explored using principal components analysis and relationships with the environmental data tested by redundancy analyses. Transfer function models were developed using a variety of techniques. As in other regions, depth to water table is the most important control on amoebae community composition. Transfer function performance was initially poor, primarily due to the inclusion of samples from areas of the site that had been heavily affected by peat cutting and had distinctly different amoebae communities. Model performance is improved by selective sample exclusion, reducing jack-knifed root mean square error of prediction to 7.1 cm. The model was tested using an initial palaeoecological data-set. Overlap with the training set was limited, although a hydrological reconstruction using this model produces similar results to a transfer function derived from northern European peatlands. This study provides the first testate amoebae transfer function from Asia and demonstrates that hydrological preferences of many of the key taxa are consistent across a large area of the Northern Hemisphere. The transfer function will allow detailed palaeoclimate reconstruction from this peatland, adding to our knowledge of Holocene climatic change in southwest Asia. © 2008, the Society of Wetland Scientists.
Abstract.
McClymont EL, Mauquoy D, Yeloff D, Broekens P, Van Geel B, Charman DJ, Pancost RD, Chambers FM, Evershed RP (2008). The disappearance of Sphagnum imbricatum from Butterburn Flow, UK.
Holocene,
18(6), 991-1002.
Abstract:
The disappearance of Sphagnum imbricatum from Butterburn Flow, UK
The disappearance of the previously abundant moss species Sphagnum imbricatum has been investigated at Butterburn Flow, northern England, using organic geochemical, elemental, macrofossil, pollen and testate amoebae analyses. Variations in the assemblage of peat-forming plants were tracked using the macrofossil distributions as well as the relative chain lengths of n-alkanes and concentrations of 5-n-alkylresorcinols and triterpenols. No significant changes to the vegetation assemblage could be detected prior to the loss of S. imbricatum. Variations in water depth were reconstructed using a testate amoebae transfer function and inferred qualitatively using bulk elemental composition and biomarkers for changing redox conditions in the bog subsurface: the degree of isomerization in the C31 hopanes, and the concentrations of bishomohopanol and archaeol. Pollen analysis reconstructed the landscape surrounding the mire and revealed evidence for human disturbance. The results suggest that bog surface wetness increased with the transition from Sphagnum imbricatum to Sphagnum magellanicum, but the increase was not large and S. imbricatum had previously survived similar periods of wetness. However, the loss of S. imbricatum coincides with increasing human disturbance surrounding the bog, which may have altered nutrient inputs to the bog surface from agriculturally derived dust, to the detriment of S. imbricatum but to the benefit of S. magellanicum and Eriophorum vaginatum. It is proposed here that the stresses imposed by the combination of changing nutrient inputs and a rapidly rising water-table drove the disappearance of S. imbricatum from Butterburn Flow at c. cal. AD 1300. © 2008 SAGE Publications.
Abstract.
Mauquoy D, Yeloff D, Van Geel B, Charman DJ, Blundell A (2008). Two decadally resolved records from north-west European peat bogs show rapid climate changes associated with solar variability during the mid-late Holocene.
Journal of Quaternary Science,
23(8), 745-763.
Abstract:
Two decadally resolved records from north-west European peat bogs show rapid climate changes associated with solar variability during the mid-late Holocene
Two 14C accelerator mass spectrometry (AMS) wiggle-match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid-late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280-1300, cal. yr AD 1640 and cal. yr AD 1790-1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10-50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2-3 yrcm-1, ∼1310 yr old, 34 14C dates) Danish profile offers an unprecedented high-resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short-lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yrcm-1, ∼5250 yr old, 42 14C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.
Abstract.
van der Linden M, Vickery E, Charman DJ, Broekens P, van Geel B (2008). Vegetation history and human impact during the last 300 years recorded in a German peat deposit.
Review of Palaeobotany and Palynology,
152(3-4), 158-175.
Abstract:
Vegetation history and human impact during the last 300 years recorded in a German peat deposit
A peat core from the Barschpfuhl kettlehole mire in north-east Germany was analysed for multiproxy indicators (plant macrofossils, pollen/non-pollen microfossils, testate amoebae, colorimetric humification, carbon/nitrogen ratios, bulk density, loss on ignition), to investigate the effects of climate change and human impact on vegetation and peat accumulation during the last c. 300 years. 14C wiggle-match dating was applied for high-precision dating. Testate amoebae assemblages were used to reconstruct past water table depths and compared with other proxies and instrumental climate data from the mid-18th century onwards. The mire hydrology of this relatively small bog was heavily influenced by forestry changes in the area. The climate signal was therefore obscured. Afforestation with fast-growing conifers and drainage for agricultural purposes resulted in a lowering of the water level, changes in trophic status, changes in mire surface vegetation and increased decomposition of the peat. Variations in the openness and cultivated land indicators in the pollen data of Barschpfuhl reflect regional population density and land use changes. © 2008 Elsevier B.V. All rights reserved.
Abstract.
2007
Charman DJ, Blundell A, Alm J, Bartlett S, Begeot C, Blaauw M, Chambers F, Daniell J, Evershed R, Hunt J, et al (2007). A new European testate amoebae transfer function for palaeohydrological reconstruction on ombrotrophic peatlands.
Journal of Quaternary Science,
22(3), 209-221.
Abstract:
A new European testate amoebae transfer function for palaeohydrological reconstruction on ombrotrophic peatlands
Proxy climate data can be obtained from reconstructions of hydrological changes on ombrotrophic (rain-fed) peatlands using biological indicators, such as testate amoebae. Reconstructions are based on transfer functions, relating modern assemblage composition to water table and moisture content, applied to fossil sequences. Existing transfer functions in Europe and elsewhere are limited geographically and there are often problems with missing or poor analogues. This paper presents a new palaeohydrological transfer function based on sampling raised mires from across Europe. Relationships between assemblages and hydrological variables are described using ordination analyses. Transfer functions are developed for depth to water table (n=119) and moisture content (n=132) with root mean squared errors (RMSEP) of 5.6 cm and 2.7% respectively. Both transfer functions have an r2 of 0.71, based on 'leave one out' cross-validation. Comparisons with an existing transfer function for Britain show that the European transfer function performs well in inferring measured water tables in Britain but that the British data cannot be used to infer water tables for other European sites with confidence. Several of the key missing and poor analogue taxa problems encountered in previous transfer functions are solved. The new transfer function will be an important tool in developing peat-based palaeoclimatic reconstructions for European sites. Copyright © 2006 John Wiley & Sons, Ltd.
Abstract.
SILLASOO U, MAUQUOY D, BLUNDELL A, CHARMAN DAN, BLAAUW M, DANIELL JRG, TOMS P, NEWBERRY J, CHAMBERS FM, KAROFELD E, et al (2007). Peat multi-proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia. Boreas, 36(1), 20-37.
Sillasoo U, Mauquoy D, Blundell A, Charman D, Blaauw M, Daniell JRG, Toms P, Newberry J, Chambers FM, Karofeld E, et al (2007). Peat multi-proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia.
Boreas,
36(1), 20-37.
Abstract:
Peat multi-proxy data from Männikjärve bog as indicators of late Holocene climate changes in Estonia
As part of a wider project on European climate change over the past 4500 years, a 4.5-m peat core was taken from a lawn microform on Männikjärve bog, Estonia. Several methods were used to yield proxy-climate data: (i) a quadrat and leaf-count method for plant macrofossil data, (ii) testate amoebae analysis, and (iii) colorimetric determination of peat humification. These data are provided with an exceptionally high resolution and precise chronology. Changes in bog surface wetness were inferred using Detrended Correspondence Analysis (DCA) and zonation of macrofossil data, particularly concerning the occurrence of Sphagnum balticum, and a transfer function for water-table depth for testate amoebae data. Based on the results, periods of high bog surface wetness appear to have occurred at c. 3100, 3010-2990, 2300, 1750-1610, 1510, 1410, 1110, 540 and 310 cal. yr BP, during four longer periods between c. 3170 and 2850 cal. yr BP, 2450 and 2000 cal. yr BP, 1770 and 1530 cal. yr BP and in the period from 880 cal. yr BP until the present. In the period between 1770 and 1530 cal. yr BP, the extension or initiation of a hollow microtope occurred, which corresponds with other research results from Männikjärve bog. This and other changes towards increasing bog surface wetness may be the responses to colder temperatures and the predominance of a more continental climate in the region, which favoured the development of bog micro-depressions and a complex bog microtopography. Located in the border zone of oceanic and continental climatic sectors, in an area almost without land uplift, this study site may provide valuable information about changes in palaeohydrological and palaeoclimatological conditions in the northern parts of the eastern Baltic Sea region.
Abstract.
Yeloff D, Charman D, van Geel B, Mauquoy D (2007). Reconstruction of hydrology, vegetation and past climate change in bogs using fungal microfossils.
Review of Palaeobotany and Palynology,
146(1-4), 102-145.
Abstract:
Reconstruction of hydrology, vegetation and past climate change in bogs using fungal microfossils
Water is one of the most important environmental factors defining the niche of terrestrial fungi, and fungi preserved in ombrotrophic peat deposits have the potential to indicate past variations in surface wetness and vegetation composition. This study aimed to assess the potential of fungal microfossils for palaeoclimate reconstructions. The environmental preferences of fungi were evaluated by assessing the relationships among fungal types, the peat-forming vegetation, the occurrence of fire, and water table status in fossil and modern samples from two raised bogs in northern England and Denmark. The microfungi which showed consistent patterns among the three datasets examined in the study were generally indicators of relatively dry (hummock-like) conditions, and the abundance of most of the abundant fungal types observed reflected the prevalent vegetation type more than the direct influence of local moisture conditions. A number of fungal microfossils were identified which can be used to consistently provide a qualitative reconstruction of past conditions on the surface of the bog, and accurately indicate shifts between relatively dry and wet local conditions. Spores, in general, provided more information about local moisture conditions than vegetative mycelia. Some of the more abundant types, particularly Type 12 spores, showed a characteristic distribution with water table depth, which was consistent between the two different sites examined in the study. These fungal types can form the basis of future quantitative reconstructions of past water table and therefore climate in ombrotrophic bogs. © 2007 Elsevier B.V. All rights reserved.
Abstract.
Charman DJ (2007). Summer water deficit variability controls on peatland water-table changes: Implications for Holocene palaeoclimate reconstructions.
Holocene,
17(2), 217-227.
Abstract:
Summer water deficit variability controls on peatland water-table changes: Implications for Holocene palaeoclimate reconstructions
Interpretation of proxy-climate records depends on a thorough understanding of the proxy-climate relationship. Peatland surface wetness records have been interpreted as reflecting changes between cool and/or wet conditions and warm and/or dry conditions. This paper analyses a high-resolution record of reconstructed water-table changes based on testate amoebae analysis in relation to instrumental weather records since AD 1775. Replicate peat records are reconciled by multiple chronological techniques and tuning, and demonstrate that the reconstructions preserve many replicable high-frequency changes. Water-table variability is highly correlated with the total seasonal moisture deficit (precipitation - evapotranspiration, P-E) expressed as the sum of all months with negative P-E. The reconstructed water-table record reflects antecedent periods of 5 or 10 years (maximum r2 = 52.4%) and proxy bog surface wetness records can therefore be interpreted as reflecting the length and intensity of the summer water deficit period. Response surfaces of the summer deficit in relation to temperature and precipitation variability support the hypothesis that the summer deficit is determined by summer precipitation in mid-latitude oceanic peatlands and that summer temperature plays a greater but still subsidiary role in higher latitude, continental settings. These relationships apply for all plausible past Holocene climate changes and future twenty-first century climate scenarios. Non-linear responses to longer-term climate states prevent the direct application of a calibration of the reconstructed water-table records to infer quantitative estimates of climate variables. Models that combine peat accumulation, mire growth and hydrological processes are required to undertake this task. © 2007 SAGE Publications.
Abstract.
2006
Hughes PDM, Blundell A, Charman DJ, Bartlett S, Daniell JRG, Wojatschke A, Chambers FM (2006). An 8500 cal. year multi-proxy climate record from a bog in eastern Newfoundland: contributions of meltwater discharge and solar forcing.
Quaternary Science Reviews,
25(11-12), 1208-1227.
Abstract:
An 8500 cal. year multi-proxy climate record from a bog in eastern Newfoundland: contributions of meltwater discharge and solar forcing
Analyses of plant macrofossils, testate amoebae and the degree of peat humification have been combined into a single composite reconstruction of bog surface wetness (BSW) on a coastal plateau bog in eastern Newfoundland. The reconstruction reveals 14 distinctive phases of near-surface water tables commencing at 8270, 7500, 6800, 5700, 5200, 4900, 4400, 4000, 3100, 2500, 2050, 1700, 600 and 200 cal. BP, which may be used to infer changes in the atmospheric water balance of eastern Newfoundland. The first two major phases of pool development follow the final drainage of glacial Lake Agassiz at 8400 cal. BP and the Ungava lakes between ca 7500-6900 cal. BP, respectively. From 7500 cal. BP to the present there appears to be a strong correlation, within dating errors, between reconstructed BSW and the stacked ice rafted debris (IRD) record in the North Atlantic Ocean. Both records may reflect long-term changes in air masses. Comparisons of the BSW reconstruction with records of cosmogenic isotope flux also suggest a persistent link between reduced solar irradiance and increased BSW during the Holocene. © 2005 Elsevier Ltd. All rights reserved.
Abstract.
Massey AC, Gehrels WR, Charman DJ, White SV (2006). An intertidal foraminifera-based transfer function for reconstructing holocene sea-level change in southwest England.
Journal of Foraminiferal Research,
36(3), 215-232.
Abstract:
An intertidal foraminifera-based transfer function for reconstructing holocene sea-level change in southwest England
Southwest England is an area of particular interest to sea-level studies as it has been argued to have the fastest subsiding coastline in the United Kingdom. However, this suggestion is based on very limited data and there is a need for quantitative sea-level estimates to establish an accurate regional Holocene sea-level history. Intertidal foraminifera are well suited as sea-level indicators due to their quantifiable relationships with tidal heights. In this study we analyze surface sediments from mudflats and salt marshes in the Erme and Salcombe-Kingsbridge estuaries, south Devon, to provide an intertidal foraminifera-based transfer function for reconstructing Holocene sea-level change in southwest England, UK. Foraminifera were identified from 113 contemporary salt-marsh and mudflat samples, spanning a vertical range between -2.6 m below and +2.6 m above mean tide level (MTL). Foraminiferal assemblages exhibit a distinct and comparable vertical zonation in both estuaries. Reophax spp. Eggerella scabra and Elphidium oceanensis live preferentially around MTL, and both Trochammina inflata and Haplophragmoides spp. are useful indicators of high marsh environments. Weighted averaging partial least squares regression analysis on dead assemblages, using height in relation to MTL as the dependent variable, produces a transfer function capable of predicting paleo-sea-level positions with a precision of ±0.285 m. The transfer function was applied to foraminiferal assemblages from a Holocene core and demonstrates that the modern data set can be used to quantify the height of Holocene sea-level index points from southwest England.
Abstract.
Massey AC, Paul MA, Gehrels WR, Charman DJ (2006). Autocompaction in Holocene coastal back-barrier sediments from south Devon, southwest England, UK.
Marine Geology,
226(3-4), 225-241.
Abstract:
Autocompaction in Holocene coastal back-barrier sediments from south Devon, southwest England, UK
The present-day elevation of superficial horizons situated above a competent basal stratum is likely to be lower than the original height of deposition. This is because sediments such as minerogenic fines and peat undergo a post-depositional reduction in volume as a result of the weight of overlying sediments, the downward movement being due to the cumulative compression of all the sediment below the level in question. This "autocompaction" can affect the palaeoenvironmental interpretation of lithofacies from which a vertical reference is required, e.g. when quantifying the height of a sea-level index point. Geotechnical theory was used to apply a correction to Holocene coastal back-barrier sediments from North Sands and Blackpool Sands in south Devon (UK) and so to return marker horizons to a level approximating their original height of deposition. In this model the total downward movement is calculated by notionally dividing the underlying soil into a number of thin (∼ 0.1 to 0.2 m) layers and calculating the individual compression in each one. The results were then summed to give the total compression. This approach can underestimate the full extent of autocompaction notably due to uncertainties arising from the behaviour of organic-rich facies and from inadequate knowledge of groundwater history. The results must be considered semiquantitative and are usually minimum estimates. Results of vertical corrections from coastal sedimentary units in south Devon range from < 0.1 m in fine-grained sediments situated above basal facies to > 1 m at contacts between minerogenic sediments and peat, increasing to > 2 m in more organic facies. © 2005 Elsevier B.V. All rights reserved.
Abstract.
Charman DJ, Blundell A, Chiverrell RC, Hendon D, Langdon PG (2006). Compilation of non-annually resolved Holocene proxy climate records: Stacked Holocene peatland palaeo-water table reconstructions from northern Britain.
Quaternary Science Reviews,
25(3-4), 336-350.
Abstract:
Compilation of non-annually resolved Holocene proxy climate records: Stacked Holocene peatland palaeo-water table reconstructions from northern Britain
The number and range of Holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade. The data density for many regions and proxies now offers the potential of robust regional-scale reconstructions that avoid the problems of records from individual sites, and improve communication between palaeoclimate subdisciplines and climate modellers. However, there are problems with chronological uncertainties and quantification of proxies, which make compilation of multiple records difficult. Here we explore a 'stacking' and 'tuning' approach to the derivation of regional records from peatland climate proxies to test its applicability to non-annually resolved terrestrial records. Twelve individual records from northern Britain based on water table reconstructions from testate amoebae analysis were divided into four regions. Records were detrended, normalised and compared within regions to identify clear correlative events. The original chronologies of the records were tuned using both these events and independent age markers. The stacked record for northern Britain indicates pronounced changes to wet conditions at 3600, 2760 and 1600 cal yr BP with more minor changes at 3060, 2050, 1260, 860, 550 and 260 cal yr BP. The main wet phases are highly correlated with mid-European lake highstands, wider North Atlantic climate change inferred from ocean and ice core records, and solar variability. Tuning and stacking of non-annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model-data comparisons. © 2005 Elsevier Ltd. All rights reserved.
Abstract.
Gehrels WR, Hendon D, Charman DJ (2006). Distribution of testate amoebae in salt marshes along the North American East Coast.
Journal of Foraminiferal Research,
36(3), 201-214.
Abstract:
Distribution of testate amoebae in salt marshes along the North American East Coast
This study describes the distribution of testate amoebae in three North American East Coast salt marshes (Leipsic River marsh, Delaware, USA; Little River marsh, Maine, USA; and Little Dipper Harbour marsh, New Brunswick, Canada). Five zones are recognized in the high salt marsh. With increasing marine influence, these zones are characterized by the following succession of dominant taxa: Valkanovia elegans, Tracheleuglypha dentata, Centropyxis cassis type, C. platystoma type and Difflugia pristis type. Most species occur in all three marshes, and their general vertical distribution is comparable. The results are also comparable with those obtained from British salt marshes, suggesting that salt-marsh testate amoebae have similar distributions on both sides of the Atlantic Ocean. The precision of the sea-level indicative value of testate amoebae in fossil salt-marsh sediments is a function of the local mean tidal range (MTR). Results of this study show that testate amoebae can indicate former sea levels with a precision of ±0.04 m in the Leipsic River marsh (MTR = 1.75 m), ±0.09 m in the Little River marsh (MTR = 2.6 m), and ±0.18 m in the Little Dipper marsh (MTR = 5.8 m).
Abstract.
Massey AC, Taylor GK, Gehrels WR, Charman DJ (2006). Electrical resistivity of coastal back-barrier sediments from south Devon, south-west England, United Kingdom.
Journal of Coastal Research,
22(5), 1179-1191.
Abstract:
Electrical resistivity of coastal back-barrier sediments from south Devon, south-west England, United Kingdom
Electrical resistivity surveying is a commonly used geophysical method in civil engineering, but few examples of this application exist in palaeoenvironmental reconstructions. Here, we provide an example of the application of the method to the two-dimensional distribution of lithofacies from coastal back-barrier sites of south-west England. The region is particularly important in coastal studies because of the current paucity of stratigraphic data and its position along the fastest subsiding coastline in Britain. Surveys were carried out at four sites along the south Devon coastline with the ABEM LUND Imaging System. Ranges of electrical resistivity of subsurface sediments were interpreted by ground-truthing from boreholes placed along the survey runs. Electrical resistivity surveys carried out at coastal locations can be affected by a range of phenomena-in particular, saltwater intrusion from rising tides and storm-induced overwash events. Conductive groundwater can cause temporal variations in the electrical profiles measured at the surface. This has not been witnessed to any significant degree at our sites. Despite anthropogenic and environmental noise (e.g. fences, tracks, drainage ditches, streams, and the possibility of salt water intrusion), the system has produced encouraging results and demonstrated that the technique has a future in coastal research. In particular, it readily identified the depth of gravel barriers and depth to basal strata. Given the speed and efficiency of data collection and interpretation available in the field, such systems should prove valuable in future research. Integration of the resistivity profiles with borehole information and radiocarbon dates of selected samples show that back-barrier basins began to fill with fine minerogenic sediments and shells ca. 9000 to 8000 Cal BP, and the majority of sites became terrestrialised by ca. 4500 Cal BP.
Abstract.
Schnitchen C, Charman DJ, Magyari E, Braun M, Grigorszky I, Tóthmérész B, Molnár M, Szántó Z (2006). Reconstructing hydrological variability from testate amoebae analysis in Carpathian peatlands.
Journal of Paleolimnology,
36(1), 1-17.
Abstract:
Reconstructing hydrological variability from testate amoebae analysis in Carpathian peatlands
Peatlands offer the potential for high resolution records of water balance over Holocene timescales, yet this potential is under-exploited in many areas of the world. Within Europe, peatlands are mostly confined to areas north of 55°N, but several areas of southern and eastern Europe contain small peatlands which may be suitable for palaeoclimatic reconstruction. In this paper we test the potential of peatlands in the Carpathian region for deriving quantified estimates of water table changes using testate amoebae analysis. A training set for palaeohydrological reconstruction from testate amoebae assemblages was obtained by collecting surface samples from 13 peatlands, including 9 from Hungary and 4 from Transylvania (Romania). Using a simple measure of mean annual water tables estimated from staining of PVC tape, we found that some peatlands were heavily influenced by runoff and groundwater, and were therefore not suitable as modern analogues of ombrotrophic climatically sensitive sites. The relationship between the testate amoebae assemblages in the modern samples and the environmental variables was explored using CCA. The CCA biplot showed that the most important variables are depth to water table and moisture content, confirming that hydrology is a key control on taxon distribution. pH was a secondary gradient. A transfer function for % moisture and depth to water table was established and applied to fossil assemblages from a sequence from Fenyves-teto, Transylvania, Romania. The reconstructed water table shows a number of variations which have parallels with other palaeoclimatic records from Europe and the North Atlantic prominent phases of higher water tables are associated with the periods 8000-8300 cal BP, 3000-2500 cal BP and after 600 cal BP. We suggest that these were periods of particular intensification of westerly airflow which affected eastern Europe as well as western and central Europe. © Springer Science+Business Media B.V. 2006.
Abstract.
Schnitchen C, Magyari E, Charman DJ, Tothmeresz B, Grigorszky I, Beres V, Braun M (2006). The possibility of reconstruction of past hydrological changes in a Sphagnum bog by the use of testate amoebae (Rhizopoda : Testacea) in the Carpathian Basin.
Author URL.
2005
Charman DJ, Garnett MH (2005). Chronologies for recent peat deposits using wiggle-matched radiocarbon ages: Problems with old carbon contamination.
RADIOCARBON,
47(1), 135-145.
Abstract:
Chronologies for recent peat deposits using wiggle-matched radiocarbon ages: Problems with old carbon contamination
Dating sediments which have accumulated over the last few hundred years is critical to the calibration of longer-term paleoclimate records with instrumental climate data. We attempted to use wiggle-matched radiocarbon ages to date 2 peat profiles from northern England which have high-resolution records of paleomoisture variability over the last similar to 300 yr. A total of 65 C-14 accelerator mass spectrometry (AMS) measurements were made on 33 macrofossil samples. A number of the age estimates were older than expected and some of the oldest ages occurred in the upper parts of the sequence, which had been dated to the late 19th and early 20th century using other techniques. We suggest that the older C-14 ages are the result of contamination by industrial pollution. Based on counts of spheroidal carbonaccous particles (SCPs), the potential aging effect for SCP carbon was calculated and shown to be appreciable for samples from the early 20th century. Ages corrected for this effect were still too old in some cases, which could be a result of fossil CO2 fixation, non-SCP particulate carbon, contamination due to imperfect cleaning of samples, or the "reservoir effect" from fixation of fossil carbon emanating from deeper peat layers. Wiggle matches based on the overall shape of the depth-C-14 relationship and the C-14 minima in the calibration curve could still be identified. These were tested against other age estimates (Pb-210, pollen, and SCPs) to provide new age-depth models for the profiles. New approaches are needed to measure the impact of industrially derived carbon on recent sediment ages to provide more secure chronologies over the last few hundred years.
Abstract.
Author URL.
Schoning K, Charman DJ, Wastegård S (2005). Reconstructed water tables from two ombrotrophic mires in eastern central Sweden compared with instrumental meteorological data.
Holocene,
15(1), 111-118.
Abstract:
Reconstructed water tables from two ombrotrophic mires in eastern central Sweden compared with instrumental meteorological data
Water-level changes for the last 125 years were reconstructed from two ombrotrophic mires in eastern central Sweden using testate amoebae assemblages. The reconstructed water tables show the same overall pattern with high water tables during the 1950s and 1960s and low water levels from the 1970s until present. The similarity in the two records supports the hypothesis that water-table changes in the ombrotrophic mires of this area are driven by climate change. Correlation of decadal means of reconstructed water levels and instrumental meteorological data was performed to examine the relationship between water table and climatic variability. The results show that the reconstructed water tables are correlated with changes in mean annual temperature (p < 0.05). This contrasts with similar data for other parts of Europe where correlations have been found with summer or annual precipitation and temperature. We suggest that low rainfall in this area of Sweden makes the peatlands more susceptible to changing temperature and that the lack of a response to precipitation is a function of low rainfall variability over the comparison period. The results show that mire surface wetness responses to climate change are spatially variable and greater attention should be given to understanding this variability if more accurate palaeoclimatic inferences are to be drawn from longer Holocene records.
Abstract.
2004
Hendon D, Charman DJ (2004). High-resolution peatland water-table changes for the past 200 years: the influence of climate and implications for management.
Holocene,
14(1), 125-134.
Abstract:
High-resolution peatland water-table changes for the past 200 years: the influence of climate and implications for management
Management of peatlands for conservation purposes is often directed at mitigation of damaging impacts of past and present human activity. Assessment of such impacts is often based on perspectives from short-term ecological data. Here we test a series of hypotheses for the causes of changes in mire hydrology and vegetation on the Border Mires in northern England using palaeoecological data for the last 200 years. Ecological data suggest peatlands surrounded by plantation forestry have become drier over the last 40 years. This could be caused by direct hydrological impacts of the growing trees and associated drainage or indirectly by the cessation of grazing and burning. A third hypothesis is that hydrological changes are the result of recent climatic change. High-resolution water-table reconstructions from testate amoebae analysis supported by plant macrofossil analysis and dated by 210Pb, spheroidal carbonaceous particles (SCPs) and pollen data demonstrate that a site outside the direct influence of forestry has also become drier during the twentieth century. This suggests that forestry is not the main cause of changes observed on other sites. Water-table declines began earlier than the main phase of forest planting and the magnitude of change appears to be similar to that on a site within the forest. Subjective comparisons of reconstructed water tables with meteorological data suggest that hydrological changes on the mires are primarily driven by summer temperature changes. If future regional climatic change predictions are correct, further water-table decline will follow and current management activities are unlikely to restore mires to their former condition.
Abstract.
Chambers FM, Charman DJ (2004). Holocene environmental change: Contributions from the peatland archive.
Holocene,
14(1), 1-6.
Abstract:
Holocene environmental change: Contributions from the peatland archive
Peatlands provide a widespread terrestrial archive of Holocene environmental change. The taphonomy of peat is relatively simple, the range of evidence and proxies is wide, and dating methods have become more accurate and precise, such that the potential temporal resolution of records is high. Although long established, the use of peatlands as archives of Holocene change has undergone phases of decline and resurgence. Here, the variable exploitation of the peat archive is explored, and recent developments in peatland science as applied to Holocene records are reviewed with reference to the collection of papers in this Special Issue of the Holocene, which are arranged in four key themes: (1) records of Holocene climatic change; (2) peatland dynamics; (3) carbon accumulation; and (4) implications for conservation and management. The changing acceptance of peatlands as archives of Holocene climatic change is attributed to developments in understanding of the peatland system and geographical differences in the history of Holocene research. Recent developments in biological and geochemical proxies combined with improvements in chronological techniques have resulted in renewed interest in peatland palaeoclimate records. Peatlands are an important global carbon pool and it is clear that climate has influenced the efficiency of long-term carbon sequestration by these systems. Climate has also had an impact on the biodiversity and condition of peatlands, which creates problems in discerning cause and effect in sites affected by human activities, and in targeting remedial management. It is concluded that particular strengths of the archive are the current diversity of peat-based palaeoenvironmental research and the potential for multiproxy analyses to be applied to a range of research issues. Mire-based investigations can complement research in other realms, and are deserving of greater attention from researchers of other archives.
Abstract.
Charman DJ, Brown AD, Hendon D, Karofeld E (2004). Testing the relationship between Holocene peatland palaeoclimate reconstructions and instrumental data at two European sites.
Quaternary Science Reviews,
23(1-2), 137-143.
Abstract:
Testing the relationship between Holocene peatland palaeoclimate reconstructions and instrumental data at two European sites
Peatland surface wetness records provide long Holocene palaeoclimate reconstructions at 101-102 year resolution. They reflect changes in water balance but the relative strength of precipitation and temperature signals are not known. In common with other non-annually resolved records, there has been no testing of the reconstructions against instrumental climate data. In this paper high-resolution records of palaeohydrological change reconstructed from testate amoebae analysis are used to examine critically the relationships between reconstructed water table change, instrumental water table and climate data. A 200-year record of reconstructed water table from northern England shows that the strongest control on reconstructed mean annual water table change is summer precipitation, with summer temperature becoming more important over longer time periods. A 50-year record from Estonia shows that both measured and reconstructed water table records are strongly correlated with summer precipitation. Summer temperature is also correlated with reconstructed water table. We conclude that peatland surface wetness records should be interpreted as primarily reflecting summer precipitation variability, with summer temperature increasingly important in more continental settings. © 2003 Elsevier Ltd. All rights reserved.
Abstract.
2003
Wilmshurst JM, Wiser SK, Charman DJ (2003). Reconstructing Holocene water tables in New Zealand using testate amoebae: Differential preservation of tests and implications for the use of transfer functions.
Holocene,
13(1), 61-72.
Abstract:
Reconstructing Holocene water tables in New Zealand using testate amoebae: Differential preservation of tests and implications for the use of transfer functions
Testate amoebae analysis is used to provide the first quantitative reconstruction of Holocene surface wetness changes from a Southern Hemisphere ombrogenous bog. Water-table depth and surface moisture are the dominant environmental factors influencing testate amoebae species composition in a modern training set of 62 surface samples from 19 bogs in New Zealand. A transfer function based on partial least squares (PLS) performed well in cross-validation of modern samples, but produced unrealistic predictions of water-table depth and moisture for fossil samples. This resulted from poor overlap of species composition between modern and fossil samples. Peat humification data is used to examine decay-related species diversity trends and ordination is used to explore the differences between modern and fossil assemblages. Poor overlap can be explained by differential preservation in the fossil assemblages of those taxa with more robust tests. This enhances their abundance and reduces the overall diversity of the fossil assemblages. Human activities over the last 150 years have also influenced the surface environments and hydrology of the sampled bogs. In this situation, weighted average (WA) and tolerance downweighted weighted average (WA-Tol) models were more robust than PLS, and were applied, along with semi-quantitative scoring, to reconstruct more realistic Holocene surface wetness changes. Selection of the best model for reconstruction of surface wetness changes should be based on the characteristics of the fossil data rather than the predictive power of the model in cross-validation of the modern data alone.
Abstract.
Smith RS, Charman D, Rushton SP, Sanderson RA, Simkin JM, Shiel RS (2003). Vegetation change in an ombrotrophic mire in northern England after excluding sheep.
Abstract:
Vegetation change in an ombrotrophic mire in northern England after excluding sheep
Abstract.
2002
Bobrov AA, Charman DJ, Warner BG (2002). Ecology of testate amoebae from oligotrophic peatlands: Specific features of polytypic and polymorphic species.
Biology Bulletin,
29(6), 605-617.
Abstract:
Ecology of testate amoebae from oligotrophic peatlands: Specific features of polytypic and polymorphic species
Relationships between species abundance and water table depth and soil moisture have been modeled using weighted averaging and species niches have been calculated as optima and tolerance for these parameters. Niche separation of closely related taxa has been examined in detail and it has been shown that there is often a gradient of hydrological preference within each taxon. Wet to dry gradients include those found in the Trigonopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), Assulina - Valkanovia group (A. seminulum > A. muscorum > V. elegans), and Trinema lineare group (T. lineare var. truncatum > T. lineare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera have been shown to consistently occur in wetter habitats than glabrous forms of those with shorter spines. A conclusion has been drawn that palaeoecological studies should cover the lowest taxa possible within these groups to maximize the ecological indicator value of the assemblages recorded.
Abstract.
Bobrov AA, Charman DJ, Warner BG (2002). Ecology of testate amoebae from oligotrophic peatlands: specific features of polytypic and polymorphic species.
Izvestiia Akademii nauk. Seriia biologicheskaia / Rossiiskaia akademiia nauk(6), 738-751.
Abstract:
Ecology of testate amoebae from oligotrophic peatlands: specific features of polytypic and polymorphic species
Relationships between species abundance and water table depth and soil moisture have been modeled using weighted averaging and species niches have been calculated as optima and tolerance for these parameters. Niche separation of closely related taxa has been examined in detail and it has been shown that there is often a gradient of hydrological preference within each taxon. Wet to dry gradients include those found in the Trigionopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), Assulina-Valkanovia group (A. seminulum > A. muscorum > V. elegans), and Trinema lineare group (T. lineare var. truncatum/T. lioneare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera have been shown to consistently occur in wetter habitats than glabrous forms of those with shorter spines. A conclusion has been drawn that palaeoecological studies should cover the lowest taxa possible within these groups to maximize the ecological indicator value of the assemblages recorded.
Abstract.
Gehrels WR, Roe HM, Charman DJ (2002). Foraminifera, testate amoebae and diatoms as sea-level indicators in UK saltmarshes: a quantitative multiproxy approach (vol 16, pg 201, 2001).
JOURNAL OF QUATERNARY SCIENCE,
17(3), 285-285.
Author URL.
Roe HM, Charman DJ, Roland Gehrels W (2002). Fossil testate amoebae in coastal deposits in the UK: Implications for studies of sea-level change.
Journal of Quaternary Science,
17(5-6), 411-429.
Abstract:
Fossil testate amoebae in coastal deposits in the UK: Implications for studies of sea-level change
Assemblages of testate amoebae in UK saltmarshes are strongly correlated with elevation and flooding duration, suggesting that if adequately preserved in sediments they may be used as accurate sea-level indicators. To examine the preservation of testate amoebae in the fossil record in coastal environments, subsamples were collected from a range of coastal sites around Britain, including saltmarsh, coastal reedswamp, isolation basin, back-barrier and coastal raised bog sites. The results showed that testate amoebae are present in the fossil record, although in variable species diversities, concentrations and states of preservation. Testate amoebae were found to be well preserved in isolation basin infills and coastal raised bog deposits, where diverse assemblages (>20 taxa) were recorded. In the upper part of the isolation basin sequence from Loch nan Corr, northwest Scotland, the testate amoebae assemblages showed a greater degree of sensitivity to transitional salinity changes than existing foraminferal and larger testate amoebae data sets. This implies that testate amoebae, particularly small to medium-sized specimens (15-300 μm), may hold considerable potential for sea-level reconstruction in these environments. Preservation of testate amoebae in a freshly sampled core of saltmarsh sediment from South Wales was reasonable, although test distribution decreased significantly in abundance below 18 cm. The assemblage composition was similar to that found in the contemporary surface environment. The preservation of testate amoebae in saltmarsh and coastal reedswamp deposits of mid-Holocene age was variable and generally poor. Partial dehydration of the sediment samples may account for this. Further studies are required to examine the palaeoecology and distribution of testate amoebae in similar coastal settings, to strengthen these preliminary findings. Copyright © 2002 John Wiley & Sons, Ltd.
Abstract.
Wilmshurst JM, McGlone MS, Charman DJ (2002). Holocene vegetation and climate change in southern New Zealand: Linkages.
Journal of Quaternary Science,
17(7), 653-666.
Abstract:
Holocene vegetation and climate change in southern New Zealand: Linkages
This paper presents a Holocene pollen record from an ombrotrophic bog in Southland, New Zealand, together with multiproxy data (testate amoebae, peat humification and plant macrofossils) from the same core to establish an independent semiquantitative record of peatland surface moisture. Linkages between reconstructed peatland surface moisture and regional forest composition are investigated using redundancy analysis of the forest pollen data constrained with predicted bog water-table depths. Over 32% of the pollen data variance can be explained by surface moisture changes in the bog, suggesting a common cause of water-table and regional vegetation change. Water tables were higher during the early to mid-Holocene when the forest was dominated by podocarp taxa. Water tables lowered after about 3300 cal. yr BP coevally with the expansion of Nothofagus species, culminating with the dominance of Nothofagus subgenus Fuscospora in the past 1200 cal. yr BP. This is in apparent opposition to the warm/dry to cool/wet trend suggested by subjective interpretation of pollen data alone, from this and other studies. We suggest that during the late Holocene, drier summers associated with shifts in solar insolation caused reduced surface wetness and summer humidity, which together with a trend to cooler winters, apparently favoured the regeneration of Nothofagus species. Copyright © 2002 John Wiley and Sons, Ltd.
Abstract.
Wilmshurst JM, McGlone MS, Charman DJ (2002). Holocene vegetation and climate change in southern New Zealand: Linkages between forest composition and quantitative surface moisture reconstructions from an ombrogenous bog.
JOURNAL OF QUATERNARY SCIENCE,
17(7), 653-666.
Author URL.
Charman DJ, Roe HM, Roland Gehrels W (2002). Modern distribution of saltmarsh testate amoebae: Regional variability of zonation and response to environmental variables.
Journal of Quaternary Science,
17(5-6), 387-409.
Abstract:
Modern distribution of saltmarsh testate amoebae: Regional variability of zonation and response to environmental variables
Sea-level reconstruction from biological indicators in saltmarsh sediments requires an understanding of the modern ecology of the organisms concerned. Previous work suggested that testate amoebae are a potential new group of organisms to use for sea-level reconstruction, especially combined with diatoms and foraminifera. This paper analyses data from three saltmarshes on the Taf estuary, South Wales, the River Erme, Devon, and at Brancaster, Norfolk (UK) to (i) test for the presence and zonation of testate amoebae in relation to elevation; (ii) examine the similarity of zonation patterns between marshes; and (iii) explore the relationship between assemblage composition and a wider range of environmental variables. In addition we provide an update on the identification of testate amoebae on saltmarshes. Our results confirm that at all sites the primary environmental gradient is tidal inundation. Major changes in taxa along the tidal gradient are similar except for the lowest elevations, where different taxa become dominant at different sites. Canonical correspondence analysis (CCA) shows that assemblage composition is also strongly related to other variables, independent of the tidal position. Salinity, particle size and organic matter content are particularly important, and there is a statistically significant geographical effect on assemblages. Relationships between sea-level and assemblage composition are often stronger for individual sites, suggesting that local data sets should be used for quantitative sea-level reconstructions. However, the combined data set would provide more robust estimates of past sea-level change from fossil data. Other environmental variables explain as much of the variability in species assemblages as tidal parameters and should be considered more often in sea-level reconstructions based on microfossil indicators. Copyright © 2002 John Wiley & Sons, Ltd.
Abstract.
Bobrov AA, Charman DJ, Warner BG (2002). [Ecology of testate amoebae from oligotrophic peatlands: specific features of polytypic and polymorphic species].
Izv Akad Nauk Ser Biol(6), 738-751.
Abstract:
[Ecology of testate amoebae from oligotrophic peatlands: specific features of polytypic and polymorphic species].
Relationships between species abundance and water table depth and soil moisture have been modeled using weighted averaging and species niches have been calculated as optima and tolerance for these parameters. Niche separation of closely related taxa has been examined in detail and it has been shown that there is often a gradient of hydrological preference within each taxon. Wet to dry gradients include those found in the Trigionopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), Assulina-Valkanovia group (A. seminulum > A. muscorum > V. elegans), and Trinema lineare group (T. lineare var. truncatum/T. lioneare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera have been shown to consistently occur in wetter habitats than glabrous forms of those with shorter spines. A conclusion has been drawn that palaeoecological studies should cover the lowest taxa possible within these groups to maximize the ecological indicator value of the assemblages recorded.
Abstract.
Author URL.
2001
Charman DJ (2001). Biostratigraphic and palaeoenvironmental applications of testate amoebae.
Quaternary Science Reviews,
20(16-17), 1753-1764.
Abstract:
Biostratigraphic and palaeoenvironmental applications of testate amoebae
Testate amoebae (also referred to as rhizopods, thecamoebians and arcellaceans) are single-celled organisms in which the cytoplasm is enclosed within an external shell (the test). They live in a wide range of terrestrial and aquatic habitats, including wet soils, lakes and saltmarshes, and fossil tests have been recovered from sediments from all these environments. This paper reviews existing and recently developed applications of testate amoebae analysis to biostratigraphic description of Quaternary sediments and palaeoenvironmental reconstruction. Advances in testate amoebae analysis are discussed for three key areas of Quaternary research and the potential for the further exploration and use of the technique is emphasised. These areas are: (1) Peatlands and palaeoclimates: Testate amoebae have been used as a new method of reconstructing palaeoclimates from ombrotrophic peats; (2) lake sediments: Testate amoebae respond to acidity levels in lakes but they may also be useful as indicators of pollution and temperature; (3) saltmarshes and sea-level change: Testate amoebae can now be added to diatoms and foraminifera as potential indicators of sea-level change. The paper concludes with an examination of future developments in testate amoebae research and highlights the need for further work to explore their full range of occurrence in Quaternary sediments. © 2001 Elsevier Science Ltd. All rights reserved.
Abstract.
Gehrels WR, Roe HM, Charman DJ (2001). Foraminifera, testate amoebae and diatoms as sea-level indicators in UK saltmarshes: a quantitative multiproxy approach.
Journal of Quaternary Science,
16(3), 201-220.
Abstract:
Foraminifera, testate amoebae and diatoms as sea-level indicators in UK saltmarshes: a quantitative multiproxy approach
The vertical distribution of foraminifera, testate amoebae and diatoms was investigated in saltmarshes in the Taf estuary (south Wales), the Erme estuary (south Devon) and the Brancaster marshes (north Norfolk), to assess the use of multiproxy indicators in sea-level reconstructions. A total of 116 samples were subjected to regression analyses, using the program CALIBRATE, with duration of tidal flooding as the dependent variable. We found that the relationship between flooding duration and taxa was strongest for diatoms and testate amoebae and weakest for foraminifera. The vertical range of testate amoebae in saltmarshes is small. Their lower tolerance limit in present-day saltmarshes occurs where tides cover the marsh less than a combined total of 7 days (1.9%) in a year. However, they are important sea-level indicators because information for sea-level reconstruction is best derived from sediments that originate in the highest part of the intertidal zone. Diatoms span the entire sampled range in intertidal and supratidal areas, whereas the upper limit of foraminifera is found very close to the highest astronomical tide level. Local training sets provide reconstructions with higher accuracy and precision than combined training sets, but their use is limited if they do not represent adequate modern analogues for fossil assemblages. Although analyses are time consuming, a regional training set of all three groups of micro-organisms yields highly accurate (r2 = 0.80) and precise (low value of root mean square error) predictions of tidal level. This approach therefore could improve the accuracy and precision of Holocene sea-level reconstructions. Copyright © 2001 John Wiley & Sons, Ltd.
Abstract.
Hendon D, Charman DJ, Kent M (2001). Palaeohydrological records derived from testate amoebae analysis from peatlands in northern England: Within-site variability, between-site comparability and palaeoclimatic implications.
Holocene,
11(2), 127-148.
Abstract:
Palaeohydrological records derived from testate amoebae analysis from peatlands in northern England: Within-site variability, between-site comparability and palaeoclimatic implications
Testate amoebae analysis was undertaken on eight cores from three mires within a restricted geographical area of northern England. This was used to assess, first, the amount of autogenically produced variability in palaeohydrological records from ombrotrophic mires, and second, to determine whether a palaeoclimatic signal can be derived from testate amoebae analysis from peatlands. Past mean annual water tables were reconstructed by calibrating the testate amoebae record with an existing transfer function. There is a good degree of replicability between the water table reconstructions for the upper peats within each site (especially since cal. AD 600) and the magnitude and timing of most changes are similar. The results show that autogenic factors have a relatively minor control on palaeohydrological records from ombrotrophic peatlands, even for marginal locations where these effects should be greatest. Records from the centres of peatlands are compared to assess the replicability of hydrological changes between the sites to determine which of these changes are attributable to climate. The major fluctuations are well replicated in all central cores, especially for the last 2000 years, suggesting that these shifts are climatically forced and that there is an increasing climatic influence through time, even at the valley mire site. Comparisons with other proxy climatic records suggest that mire surface wetness changes occurred in concert across a broad region of northern England and southern Scotland during at least the last 2000 years.
Abstract.
Charman DJ, Caseldine C, Baker A, Gearey B, Hatton J, Proctor C (2001). Paleohydrological records from Peat profiles and speleothems in Sutherland Nortwest Scotland.
Quaternary Research,
55(2), 223-234.
Abstract:
Paleohydrological records from Peat profiles and speleothems in Sutherland Nortwest Scotland
Paleohydrological changes during the late Holocene are inferred from humification testate amoebae and pollen evidence from three blanket peat profiles in northwest Scotland. Replicate peat humification records from the Traligill basin share the same patterns of change for a 600-yr period of overlap between 1800 and 2400 cal yr B.P. The shared patterns inferred from samples with a resolution of 5-13 yr represent basinwide hydrological changes. In a nearby but hydrologically separate area with caves beneath peat the luminescence emission wavelength measured in two speleothem samples correlated with the humification record in the overlying peat. This correlation implies that speleothem luminescence emission wavelength depends primarily on decay rates in the soils from which drip waters are derived as long as there is no major change in soil or vegetation. The peat and speleothem records from the cave site further correlate with the peat records from the Traligill basin. Taken together the records thus represent a regional climatic signal. Peaks in surface wetness replicated in two or more records occur at ca. 2300 2090 2030 1820 1600 and 1440 cal yr B.P. Further peaks occur at 800 570 and 115 cal yr B.P. in the humification and stalagmite records that extend to the present day. Correlative changes have been observed not only in other peat records from Scotland but also in ice accumulation at GISP2. These further correlations imply that precipitation regimes in Scotland and Greenland were in phase during the late Holocene. © 2001 University of Washington.
Abstract.
2000
Caseldine CJ, Baker A, Charman DJ, Hendon D (2000). A comparative study of optical properties of NaOH peat extracts: Implications for humification studies.
Holocene,
10(5), 649-658.
Abstract:
A comparative study of optical properties of NaOH peat extracts: Implications for humification studies
Assessment of the degree of decay of peat (humification) in ombrotrophic mires has become a standard technique for palaeoclimatic reconstruction, based on the finding that decay is primarily determined by surface wetness and temperature at the time of peat deposition. Determination of humification is undertaken by colorimetric measurement of an alkali extract of the peat at 540 nm. Humification is proportional to the amount of humic matter dissolved by this extraction process, although few researchers convert results to a quantitative measure of humification expressing results as percentage light transmission through the peat. This paper uses luminescence spectroscopy to assess the chemical composition of these extracts. Luminescence excitation and emission wavelengths suggest that high molecular weight acids ('humic acids') are altered by the extraction procedure to form lower molecular weight acids ('fulvic acids'), amino acids and polysaccharides. Percentage transmission is principally related to luminescence emission wavelength and thus to molecular weight of the compounds present. Luminescence emission shows much more sensitivity to peat composition and demonstrates that different plant species may be affected to different degrees by the NaOH extraction process. The findings broadly support the underlying principle of colorimetric determination of 'humification' whereby transmission levels decrease with increasing plant breakdown, but show that it is based on an inadequate understanding of the chemical processes occurring in peat decay and preparation procedures. Luminescence spectroscopy provides a technique for resolving these issues.
Abstract.
Charman DJ, Hendon D (2000). Long-term changes in soil water tables over the past 4500 years: Relationships with climate and North Atlantic atmospheric circulation and sea surface temperature.
Climatic Change,
47(1-2), 45-59.
Abstract:
Long-term changes in soil water tables over the past 4500 years: Relationships with climate and North Atlantic atmospheric circulation and sea surface temperature
A record of mean annual water table changes in England over the past 4500 years is derived from a transfer function applied to protozoan assemblages in peat profiles. A 100-year running mean value based on three profiles shows short-term changes which are closely related to instrumental records of mean annual temperature changes (past 300 yr) and documentary records of summer wetness and winter severity (past 900 yr). Long-term (> 1000 yr) changes in this composite record are positively correlated with the GISP2 ice accumulation record, suggesting moisture budgets were in phase across the North Atlantic region over at least the last 2000 years and probably changed due to north-south movements of major pressure centres. This hypothesis is further supported by comparisons with indicators of sea surface temperature and ocean circulation. Existing regional climate predictions may underestimate the impact of future warming on soil moisture status, with significant implications for agriculture and water supply in northwestern Europe.
Abstract.
Gearey BR, Charman DJ, Kent M (2000). Palaeoecological evidence for the prehistoric settlement of Bodmin Moor, Cornwall, southwest England. Part I: the status of woodland and early human impacts.
Journal of Archaeological Science,
27(5), 423-438.
Abstract:
Palaeoecological evidence for the prehistoric settlement of Bodmin Moor, Cornwall, southwest England. Part I: the status of woodland and early human impacts
Bodmin Moor is one of the most complete and best preserved upland prehistoric landscapes in Britain. The field archaeology has been described in some detail, although on the basis of comparatively little excavation, but this has nevertheless been used to generate hypotheses concerning the nature and timing of human settlement and impacts on the Moor. In contrast, there has been relatively little palaeoenvironmental work, due to a perceived lack of suitable deposits. These two articles present new palynological data from a series of recently discovered undisturbed profiles. This first paper describes the physical and archaeological settings of the sites and discusses the nature of the early Holocene vegetation on the Moor. Although previous work has suggested a dominance of open moorland throughout the Holocene, the two high-altitude (280 m OD) profiles presented here show that dense woodland dominated by Corylus avellana and Quercus was present until around 6500 BP and probably extended to the very highest points of the Moor. Other taxa, such as Ulmus, Betula, and Tilia cordata, were also subordinate components of the vegetation. Alnus glutinosa became established later, possibly after disturbance to the vegetation by human activity, although the nature and extent of Mesolithic disturbance to the vegetation is unclear. Thus, the early Holocene vegetation of the Moor was not predominantly open heath or grassland as has previously been assumed, but more probably a dense cover of hazel and oak woodland. (C) 2000 Academic Press.
Abstract.
Gearey BR, Charman DJ, Kent M (2000). Palaeoecological evidence for the prehistoric settlement of Bodmin Moor, Cornwall, southwest England. Part II: Land use changes from the Neolithic to the present.
Journal of Archaeological Science,
27(6), 493-508.
Abstract:
Palaeoecological evidence for the prehistoric settlement of Bodmin Moor, Cornwall, southwest England. Part II: Land use changes from the Neolithic to the present
Radiocarbon-dated pollen sequences from two areas of Bodmin Moor-Rough Tor in the north-west and the East Moor-are presented and the evidence for settlement in the prehistoric period on the moor considered. The nature and extent of human impact in the two areas are compared and the evidence for anthropogenic activity in the environmental record is related to that deduced from the archaeology. A tentative model of settlement and land use from the Neolithic to the Iron Age is proposed, with early activity in the Neolithic leading to a peak of settlement in the Bronze Age and continuing activity on the moor during the Iron Age and into the Romano-British period. Human activity may have begun in the earliest Neolithic and was possibly associated with construction of the hill top enclosure at Rough Tor. The Bronze Age peak of activity that is apparent in the archaeology is also represented in the palynological record. Activity in the Iron Age and later shows that the moorland was intensively used for grazing and probably hay production until settlement expanded back onto the uplands in the medieval period. This last phase resulted in the impoverishment of the soils and development of the current acid grassland and heath dominated vegetation of the moor. Finally, various suggestions are made for future research into the palaeoecology of Bodmin Moor. (C) 2000 Academic Press.
Abstract.
1999
Charman DJ, Grattan J (1999). An assessment of discriminant function analysis in the identification and correlation of distal Icelandic tephras in the British Isles.
Geological Society Special Publication,
161, 147-160.
Abstract:
An assessment of discriminant function analysis in the identification and correlation of distal Icelandic tephras in the British Isles
This paper is part of the special publication No.161, Volcanoes in the Quaternary (eds: C.R. Firth and W.J. McGuire). This paper assesses the potential of discriminant function analysis (DFA) for tephrochronology in the UK and Ireland. Current identification and correlation of Holocene tephras relies largely on radiocarbon dating to suggest a likely candidate eruption followed by a geochemical comparison using binary and ternary plots of selected major oxides. As more tephras are discovered, and the patterns of deposition appear increasingly complex, this approach is likely to work less effectively. In addition, the utility of tephra for the establishment of chronozones will be limited by the availability of radiometric dates to constrain the initial candidate eruption. The results of a DFA on some of the limited published geochemical data are presented and it is clear that this statistical technique offers advantages to the application and development of tephrochronology in western Europe. Future work should concentrate on the provision of discriminant functions from a more complete reference dataset, which will enable the identification of unknown tephras with a known probability of misclassification.
Abstract.
Charman DJ, Aravena R, Bryant CL, Harkness DD (1999). Carbon isotopes in peat, DOC, CO <inf>2</inf> , and CH <inf>4</inf> in a holocene peatland on Dartmoor, southwest England.
Geology,
27(6), 539-542.
Abstract:
Carbon isotopes in peat, DOC, CO 2 , and CH 4 in a holocene peatland on Dartmoor, southwest England
Carbon gases with younger 14 C ages than those of the surrounding peat have been reported from continental boreal peatlands, a fact which suggests that significant movement of CO 2 , CH 4 , or DOC (dissolved organic carbon) and export of C via subsurface processes are not accounted for in most estimates of contributions to the C cycle. This paper tests the hypothesis that similar processes can occur in oceanic ombrotrophic mires where water and gas movement is theoretically minimal. Measurements of 14 C and δ 13 C in CO 2 , CH 4 , and DOC, and of tritium, are reported from depths to 250 cm at Tor Royal, a raised mire in southwest England. Radiocarbon ages of gases are 1460 to 500 yr younger than those of peat from the same depths, and CO 2 is consistently younger than CH 4. DOC is 1260 to 830 yr younger than the peat, and significant amounts of tritium were found at all depths. Gas ages are mostly intermediate between the age of the peat and that of the DOC, which suggests that C is principally transported as DOC. However, some gases are younger than their associated DOC, which implies that movement of dissolved gases may also take place. δ 13 C values in gases suggest that CO 2 reduction is the major pathway for CH 4 production. Transport of C in deep peats is likely to be a significant component in the overall C budget of ombrotrophic oceanic peatlands, and C export via discharge to ground or surface waters may be an important mechanism for gaseous C emissions.
Abstract.
Charman DJ, Aravena R, Bryant CL, Harkness DD (1999). Carbon isotopes in peat, DOC, CO2, and CH4 in a holocene peatland on Dartmoor, southwest England. Geology, 27(6), 539-542.
Charman DJ, Aravena R, Bryant CL, Harkness DD (1999). Carbon isotopes in peat, DOC, CO2, and CH4 in a holocene peatland on Dartmoor, southwest England. Geology, 27(6), 539-542.
Bobrov AA, Charman DJ, Warner BG (1999). Ecology of testate amoebae (Protozoa: Rhizopoda) on peatlands in western Russia with special attention to niche separation in closely related taxa.
Protist,
150(2), 125-136.
Abstract:
Ecology of testate amoebae (Protozoa: Rhizopoda) on peatlands in western Russia with special attention to niche separation in closely related taxa.
Testate amoebae (Protozoa: Rhizopoda) are frequently used as indicators of past environmental changes, and the interpretation of fossil assemblages depends upon our knowledge of ecological affinities of taxa in modern environments. A variety of taxonomic approaches have been used in fossil studies, mostly involving grouping of closely related taxa. This paper presents data from peatlands in western Russia relating surface wetness parameters to species occurrence. Relationships between species abundance, water table depth and soil moisture are modelled using weighted averaging, and species niches are calculated as optima and tolerance for these parameters. Niche separation of closely related taxa is examined in detail and it is shown that there is often a gradient of hydrological preference within each group of taxa. Wet to dry gradients include those found in the Trigonopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), the Assulina-Valkanovia group (A. seminulum > A. muscorum > V. elegans), and the Trinema lineare group (T. lineare var. truncatum/ T. lineare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera are shown to consistently occur in wetter habitats than glabrous forms or those with shorter spines. It is concluded that palaeoecological studies should attempt the lowest taxonomic divisions possible within these groups, to maximise the ecological indicator value of the assemblages recorded.
Abstract.
Author URL.
Grattan J, Gilbertson D, Charman D (1999). Modelling the impact of Icelandic volcanic eruptions upon the prehistoric societies and environment of northern and western Britain.
Geological Society Special Publication,
161, 109-124.
Abstract:
Modelling the impact of Icelandic volcanic eruptions upon the prehistoric societies and environment of northern and western Britain
This paper is part of the special publication No.161, Volcanoes in the Quaternary (eds: C.R. Firth and W.J. McGuire). Many studies now address the impact of Icelandic volcanic eruptions upon the societies and environment of Britain and Ireland. It has become apparent that the assumptions of the magnitude of volcanic impact inherent in these studies are open to question. The scale of climatic change following many eruptions has been observed to be ephemeral or non-existent, whilst the impact of toxic volatile gases and aerosols is dependent, to a large degree, on the vulnerability of the receptor rather than the scale of deposition. The scale and extent of volcanic climatic-forcing mechanisms are examined and the popular perception of the effectiveness of these is challenged. In particular, the concepts of harsh volcanic winters and cool volcanic summers is examined via case studies of the impacts of the three largest eruptions of recent and historical times, i.e. those of the Laki fissure, Tambora and Mount Pinatubo. Alternative volcanic forcing mechanisms for environmental change are considered, principally those concerned with the transport and deposition of toxic volatile material. The need for caution in the adoption of these models is also urged. It is suggested that workers in this field need to adopt a clearer theoretical framework when contemplating the association of palaeoenvironmental data and volcanic events. Such a framework is proposed.
Abstract.
Charman DJ, Hendon D, Packman S (1999). Multiproxy surface wetness records from replicate cores on an ombrotrophic mire: Implications for Holocene palaeoclimate records.
Journal of Quaternary Science,
14(5), 451-463.
Abstract:
Multiproxy surface wetness records from replicate cores on an ombrotrophic mire: Implications for Holocene palaeoclimate records
Ombrotrophic mires can provide records of palaeoclimate over the mid- to late-Holocene in several areas of the world. Their potential is currently partly limited by difficulties with scaling indices based on plant macrofossils and humification, and the need to account for the internal variability of the mire system. This paper explores the use of testate amoebae analysis as a third technique and assesses the minimum within-site variability by comparing results from two closely spaced cores. Reconstruction of surface wetness changes was carried out on cores from the centre of an intermediate raised-blanket mire, Coom Rigg Moss, Northumberland, by analysis of testate amoebae, plant macrofossils and humification. Surface wetness changes were expressed as mean annual water table changes inferred from testate amoebae assemblages, two separate indices based on plant macrofossils and percentage transmission of humification extracts. Comparisons between the proxies suggest good agreement of general trends in Sphagnum peats but some differences in monocot and ericaceous peats. The magnitude of surface wetness changes also differs within Sphagnum peats. The records from the separate cores converge over time and replicability between cores is best in the last 1000 yr. Changes over this period are similar to those shown by estimates based on documentary sources. Good agreement is obtained between a normalised plant macrofossil index and normalised reconstructed water-table values and it is suggested that this approach could form the basis for improved composite, multiproxy records from peatlands.
Abstract.
Baker A, Caseldine CJ, Gilmour MA, Charman D, Proctor CJ, Hawkesworth CJ, Phillips N (1999). Stalagmite luminescence and peat humification records of palaeomoisture for the last 2500 years.
Earth and Planetary Science Letters,
165(1), 157-162.
Abstract:
Stalagmite luminescence and peat humification records of palaeomoisture for the last 2500 years
Recent research has suggested that both raised and blanket bogs can provide proxy climate signals from variations in peat humification. In particular, oceanic margin sites have provided sensitive records that demonstrate century scale variations in humification. However, previous research has not compared records of peat humification with other terrestrial palaeoclimate proxies. Here, two records of climate change from an oceanic marginal site in NW Scotland are analysed. One, from a blanket bog, is derived from peat humification and covers the period 2100-100 BP. A second, from two stalagmites in a cave overlain by the bog, is derived from stalagmite luminescence wavelength variations for the samples deposited over 2500-0 BP. Both peat humification and stalagmite luminescence records demonstrate 90-100 year oscillations in bog wetness, that are attributed to variations in rainfall intensity or totals over this time period. It is argued that this is probably generated by a southward shift of the path of northern hemisphere depression tracks, possibly linked to variations in solar output.
Abstract.
Charman DJ (1999). Testate amoebae and the fossil record: Issues in biodiversity.
Abstract:
Testate amoebae and the fossil record: Issues in biodiversity
Abstract.
1998
Charman D, Elmes A (1998). A Computer-based Formative Assessment Strategy for a Basic Statistics Module in Geography.
Abstract:
A Computer-based Formative Assessment Strategy for a Basic Statistics Module in Geography
Abstract.
Woodland WA, Charman DJ, Sims PC (1998). Quantitative estimates of water tables and soil moisture in Holocene peatlands from testate amoebae.
Holocene,
8(3), 261-273.
Abstract:
Quantitative estimates of water tables and soil moisture in Holocene peatlands from testate amoebae
Changes in surface wetness on Holocene ombrotrophic mires have principally been estimated from plant macrofossils and humification. Testate amoebae (Protozoa: Rhizopoda) provide an additional technique and have the potential to provide improved quantitative estimates of water-table depths and soil moisture. The relationship between hydrology and testate amoebae assemblages from 163 samples on nine British mires is explored using canonical correspondence analysis (CCA). Mean annual water-table depth and percentage soil moisture are two of the most important environmental variables related to the distribution of testate amoebae within peat. Transfer functions for these variables are developed using four underlying models; weighted averaging (WA), tolerance downweighted weighted averaging (WA-Tol), weighted averaging partial least squares (WA-PLS) and partial least squares (PLS). In 'jack-knifed' validation, WA produced the lowest prediction errors for water table, but was outperformed by WA-Tol for percentage moisture. WA and WA-Tol based transfer functions are then applied to a fossil data set from Bolton Fell Moss, Cumbria. This methodology offers a new technique for reconstructing surface wetness changes on British ombrotrophic and oligotrophic mires and provides data in terms of a meaningful environmental parameter. The cosmopolitan distribution of testate amoebae species suggests that the technique has a much wider geographical potential.
Abstract.
Charman DJ, Roe HM, Gehrels WR (1998). The use of testate amoebae in studies of sea-level change: a case study from the Taf Estuary, south Wales, UK.
Holocene,
8(2), 209-218.
Abstract:
The use of testate amoebae in studies of sea-level change: a case study from the Taf Estuary, south Wales, UK
Micropalaeontological techniques play an important role in high-resolution studies of sea-level change. Salt-marsh foraminifera are among the most valuable groups of sea-level indicators as their distribution shows a narrow vertical zonation which can be accurately related to former sea level. This paper focuses on testate amoebae ('thecamoebians'), a closely related group of protozoans which have also been widely reported in salt marshes, but only in low numbers and diversities and only in the size fraction used in foraminiferal analyses (>63 μm). A new preparation technique is described which is based on the analysis of the 63 μm) to 36 (
Abstract.
1997
West S, Charman DJ, Grattan JP, Cherburkin AK (1997). Heavy metals in Holocene Peats from south west England: Detecting mining impacts and atmospheric pollution.
Abstract:
Heavy metals in Holocene Peats from south west England: Detecting mining impacts and atmospheric pollution
Abstract.
Charman DJ (1997). Modelling hydrological relationships of testate amoebae (Protozoa: Rhizopoda) on New Zealand peatlands.
Journal of the Royal Society of New Zealand,
27(4), 465-483.
Abstract:
Modelling hydrological relationships of testate amoebae (Protozoa: Rhizopoda) on New Zealand peatlands
Research in the Northern Hemisphere shows the principal control on species distribution and abundance of testate amoebae to be local hydrology, which in ombrotrophic mires is linked directly to climate Fossil faunas can therefore be used to infer past hydrological and climatic conditions This study investigates whether a similar relationship can be found for New Zealand peatlands, as a first step towards developing a method for palaeomoisture reconstructions Fifty‐seven samples from 13 peatlands were analysed for testate amoebae and related to site hydrology, pH and conductivity of mire waters, climate, and vegetation type using canonical correspondence analysis (CCA) Water table and soil moisture were the dominant factors, and their relationship with species assemblage was modelled using four transfer functions weighted averaging (WA), tolerance downweighted weighted averaging (WA‐Tol), partial least squares (PLS), and weighted average partial least squares (WA‐PLS) PLS and WA‐PLS performed best, and suggest that palaeohydrology could be accurately inferred from fossil faunas Results are contrasted with those found in the northern peatlands. © 1997 Taylor and Francis Group, LLC.
Abstract.
Gearey BR, West S, Charman DJ, Gerrard CM, Youngs SM, Williams D, Vince A, McNeill TE, Pringle M, Stocker D, et al (1997). Notes and News. Medieval Archaeology, 41(1), 195-240.
Charman DJ, Warner BG (1997). The ecology of testate amoebae (Protozoa:Rhizopoda) in oceanic peatlands in Newfoundland, Canada: Modelling hydrological relationships for palaeoenvironmental reconstruction.
Ecoscience,
4(4), 555-562.
Abstract:
The ecology of testate amoebae (Protozoa:Rhizopoda) in oceanic peatlands in Newfoundland, Canada: Modelling hydrological relationships for palaeoenvironmental reconstruction
Peatland testate amoebae are important indicators of hydrology in fossil studies. The direct quantitative application of this principle has been limited due to a lack of suitable modern data and statistical techniques. This study gives results on the ecological relationships of testate amoebae faunas from Newfoundland, Canada, and explores techniques for modelling the relationship with water table depth. Water table, soil moisture and pH are the dominant influences on species composition in 60 samples from 14 peatland areas. Forty species occurred in > 6 samples and these are used to model the relationship with water table depth. Several models were tested. Tolerance downweighted weighted averaging (WA-Tol), weighted averaging with partial least squares (WA-PLS) and partial least squares (PLS) were assessed by jack-knifed error estimates. WA-Tol out-performed all other models and had an RMSE of 6.32 cm with a maximum bias along the gradient of 5.20 cm. WA-ToI probably performs better because the relatively high tolerance values of some species have less influence on the reconstructed values. A series of good indicator species can be identified on the basis of their narrow tolerances. These are Arcella discoides, Difflugia bacillifera, Nebela carinata, Cryptodifflugia sacculus, Nebela griseola, Nebela marginata, Quadrulella symmetrica, Amphitrema stenostoma, and Sphenoderia lenta. The analyses suggest that accurate quantitative reconstructions of past water tables are possible using these techniques and that experimentation with different models is worthwhile to improve their predictive capacity. In order to avoid problems with poor analogues, reconstructions should be based on larger more comprehensive data sets of modern faunas from a wider region.
Abstract.
Hendon D, Charman DJ (1997). The preparation of testate amoebae (Protozoa: Rhizopoda) samples from peat.
Holocene,
7(2), 199-205.
Abstract:
The preparation of testate amoebae (Protozoa: Rhizopoda) samples from peat
The analysis of testate amoebae (Protozoa: Rhizopoda) in peat is proving to be a useful new quantitative technique for assessing hydrological change on peatlands. Preparation experiments were carried out on peat extracted from Coom Rigg Moss, Northumberland, England, in order to assess the impact of different procedures on the concentration and species composition of the faunas. Five replicates of each of six samples were treated by different techniques and the testate amoebae counted together with 200 Lycopodium spores. All preparation procedures suitable for pollen extraction reduce the number of tests recorded by up to 80% and the number of taxa recorded by 60%. KOH digestion did not destroy tests but damages them, making identification difficult, although it enabled extraction of a higher number os tests. A simple water-based preparation, with sieving to remove coarse and fine detritus, appears to give the best results and is an improvement on earlier techniques in removing more extraneous material from the samples. Testate amoebae counts from samples prepared for pollen analysis must be viewed with extreme caution and are unrepresentative of the faunal content of the peat in both absolute and relative terms.
Abstract.
1996
Charman D (1996). Holocene book reviews: Palaeoecological events during the last 15000 years: regional syntheses of palaeoecological studies of lakes and mires in Europe Edited by B.E. Berglund, H.J.B. Birks, M. Ralska-Jasiewiczowa and H.E. Wright, Chichester: John Wiley, 1996, 764 pp. £100, hardback. ISBN 0-471-95840-9. The Holocene, 6(4), 499-499.
1995
Charman DJ, West S, Kelly A, Grattan J (1995). Environmental change and tephra deposition: the strath of Kildonan, Northern Scotland.
Journal of Archaeological Science,
22(6), 799-809.
Abstract:
Environmental change and tephra deposition: the strath of Kildonan, Northern Scotland
Pollen analysis, tephra counts and geochemical data are presented from the upper 200 cm of a core from a basin mire in the Strath of Kildonan, northern Scotland. Three main tephra concentrations are located and tentatively dated to c. 7650 bp (K1), c. 4250 bp (K2) and 3250 bp (K3) by cross correlation with the regional pollen chronology. The identity of the tephra layers is unknown but the peak at 4250 bp may be from the Hekla 4 eruption. The associated changes in catchment soils and vegetation are highly variable. K1 is associated with a major vegetation disturbance but no significant change occurs at K3. K2 is correlated with a large regional rise in pine pollen. These results conflict with previous studies on distal impacts of volcanic activity during the Holocene and demonstrate the diversity of environmental changes associated with Holocene volcanic activity. © 1995.
Abstract.
Charman DJ, Fullerton H (1995). Interactive lectures: a case study in a geographical concepts course.
Journal of Geography in Higher Education,
19(1), 57-68.
Abstract:
Interactive lectures: a case study in a geographical concepts course
Philosophical concepts in geography are widely regarded as an important element in geography degrees, yet students have considerable problems in understanding them, appreciating their value and applying and integrating them into the rest of their work. Part of an existing large lecture course was modified primarily to promote student understanding by increasing interaction between lecturer and student. Lecture notes were made available to the students in advance of each session, group discussions and feedback were incorporated, and opportunities were made available for verbal and written questions to be asked. The effectiveness of these efforts was evaluated by student questionnaires. One lecture was observed by a staff developer and the resulting notes are discussed from the point of view of the lecturer and the staff developer. © 1995, Taylor & Francis Group, LLC. All rights reserved.
Abstract.
Charman DJ, Pollard AJ (1995). Long-term vegetation recovery after vehicle track abandonment on Dartmoor, SW England, U.K.
Journal of Environmental Management,
45(1), 73-85.
Abstract:
Long-term vegetation recovery after vehicle track abandonment on Dartmoor, SW England, U.K
The use of extensive track networks on northern Dartmoor has caused considerable damage to vegetation during the past 24 years. The number and use of tracks has increased over this period. This paper describes the natural recovery of vegetation on tracks abandoned at several times in the past on five different sites. The undamaged vegetation varies from Agrostis grassland to wet moorland dominated by Calluna vulgaris and/or Molinia caerulea. Analysis of environmental parameters shows that the most recently used tracks suffer compaction and reduced soil depth and moisture. Canonical Correspondence Analysis (CCA) is used to explore these effects further, and the way in which vegetation can be expected to change over time is deduced from comparison of tracks of different "ages" as a "time-track" on an ordination diagram. Recovery may be rapid in grassland and heathland sites but areas of higher moorland and blanket bog recover more slowly and may never revert to their original vegetation composition. The results are discussed with respect to practical conservation management of the area. © 1995 Academic Press Ltd.
Abstract.
Charman DJ (1995). Patterned fen development in northern Scotland: Hypothesis testing and comparison with ombrotrophic blanket peats.
Journal of Quaternary Science,
10(4), 327-342.
Abstract:
Patterned fen development in northern Scotland: Hypothesis testing and comparison with ombrotrophic blanket peats
Patterned fens are part of the diverse Holocene peatland landscape of the Flow Country, northern Scotland. Their present vegetation and morphology allies them with boreal systems in Scandinavia and North America. However, previous work has shown that their mode of formation is rather different and has suggested a developmental model in which the poor fens have formed only recently and have arisen as a result of local hydrological change. These ideas are tested here by morphological, stratigraphical and macrofossil studies on three additional patterned fens covering a wider geographical and ecological range. Two sites corroborate the hypotheses of the earlier study, and one site which refutes the earlier findings can be shown to be dependent on different topographic controls. A comparison of two patterned fens with an ombrotrophic mire site in the same area shows that hydroseral processes dominate the early development of individual components of the mire complex. The time of initiation of patterned fens coincides with increasing surface wetness on the ombrotrophic mire. This may be due to climatic change and/or the coalescence of the constituent parts of the present integrated blanket mire system. The hydrological changes arising from this led to the emergence of the springs that currently supply the patterned fens with their water and elevated nutrient levels. The study supports the idea that landscape‐scale research and conservation are essential for the understanding and hydrological integrity of blanket mire landscapes such as the Flow Country. Copyright © 1995 John Wiley & Sons, Ltd
Abstract.
1994
Charman DJ, Aravena R, Warner BG (1994). Carbon dynamics in a forested peatland in north-eastern Ontario, Canada. Journal of Ecology, 82(1), 55-62.
CHARMAN DJ (1994). GEOLOGICAL CONSERVATION OF HOLOCENE PEATLANDS IN THE NATIONAL PARKS OF ENGLAND AND WALES.
Author URL.
Charman D (1994). Holocene book reviews : Mires: process, exploitation and conservation, Edited by A.L. Heathwaite and Kh. Göttlich Chichester: John Wiley, 1993, 506 pp. £79.95 ISBN 0-471-93353-8. The Holocene, 4(4), 439-439.
Charman D (1994). Holocene book reviews : the patterned peatlands of Minnesota. The Holocene, 4(1), 110-111.
WARNER BG, CHARMAN DJ (1994). Holocene changes on a peatland in northwestern Ontario interpreted from testate amoebae (Protozoa) analysis.
Boreas,
23(3), 270-279.
Abstract:
Holocene changes on a peatland in northwestern Ontario interpreted from testate amoebae (Protozoa) analysis
Radiocarbon‐dating and analyses of fossil testate amoebae (Protozoa) have established changes in soil moisture conditions on the developing surface of a Sphagnum ‐dominated peatland near Emo in northwestern Ontario. The distribution and composition of modern testate amoebae communities were studied from peatlands in the region of Ontario and Minnesota as a guide to interpreting fossil assemblages. Although the core spans all of the Holocene, fossil testate amoebae were recovered only from the part post‐dating 6500 BP. Earliest testate amoebae assemblages associated with bryophytic and cyperaceous‐rich fen peat are dominated by species in the genera Cyclopyxis and Centropyxis. By 5000 BP, Amphitrema Jraaum, Assulina muscorum, Heleopera sphugni and Hyalosphenia subjaoa become important species as Sphagnum‐rich peat accumulated at the site. Present‐day microtopographic differentiation probably developed during historic time when the site became progressively drier, as indicated by a change of Nebela griseola, N. militaris and Trigonopyxis arcula. Although it is possible to derive quantitative estimates of changing soil moisture conditions from testate amoebae, care should be taken in interpreting results, particularly from non‐Sphagnum‐rich peats, until more is learned about the distribution and ecology of modern faunas. Copyright © 1994, Wiley Blackwell. All rights reserved
Abstract.
CHARMAN DJ (1994). Late‐glacial and Holocene vegetation history of the Flow Country, northern Scotland.
New Phytologist,
127(1), 155-168.
Abstract:
Late‐glacial and Holocene vegetation history of the Flow Country, northern Scotland
The vegetation history of an important conservation area, the Flow Country in northern Scotland, is described using the results of pollen analysis from two closely spaced cores from the Cross Lochs, eastern Sutherland. Buried lake sediments and shallower surface peats yield a continuous record covering the Devensian Late‐glacial and the Holocene. The earliest Late‐glacial pollen spectra recovered suggest a transition from open habitat to more stable communities, dominated by Empetrum heath. This Windermere Interstadial vegetation shows some variability, with a phase of increased growth of juniper and birch, followed by deteriorating climate and less stable soil conditions in the transition to the Stadial, with Huperzia selago and Salix. There are poorly defined Loch Lomond Stadial and Stadial‐Holocene transition periods, characterized by Rumex/Oxyria, after which much warmer, Holocene conditions occur, with a succession of birch‐juniper and birch‐hazel woodland. Birch persists in small amounts locally, but the presence of other arboreal pollen is thought to be mostly due to long distance pollen transport. From c. 5500 BP, the landscape is largely treeless, apart from a brief phase of local pine forest c 4500–4000 BP. These changes are compared with other pollen records for northern Scotland. The trends in the Late‐glacial vegetation are broadly similar to those displayed by other sites, although many of the changes appear to be less extreme than for areas to the south and west. The lack of Artemisia during the Loch Lomond Stadial in the east Sutherland and Caithness area is particularly noteworthy. This may imply more extensive snow cover. The early Holocene is similar to the rest of northern Scotland, but invasion of Betula was more rapid and the later growth of this genus and hazel was not so dense. The lack of pine in the early Holocene allies the site with eastern Caithness and the Northern Isles, rather than north‐west Scotland and the Grampians. It is suggested that the effects of early human populations on such marginal forest areas may have been underestimated in the past. The paradoxical existence of pine macrofossils with no pollen evidence in several areas of Scotland is explained, at least in part, by the lack of temporal precision of pollen diagrams rather than by low pollen productivity, extremely localized occurrences of the species or strong prevailing winds. Copyright © 1994, Wiley Blackwell. All rights reserved
Abstract.
Grattan J, Charman DJ (1994). Non-climatic factors and the environmental impact of volcanic volatiles: Implications of the Laki fissure eruption of AD 1783. Holocene, 4(1), 101-106.
Charman DJ (1994). Patterned fen development in northern Scotland: developing a hypothesis from palaeoecological data.
Journal of Quaternary Science,
9(3), 285-297.
Abstract:
Patterned fen development in northern Scotland: developing a hypothesis from palaeoecological data
The recent discovery and description of patterned fens in Scotland has raised questions about their origins and development. A series of possible developmental models has been derived which are tested using data from a well‐developed site in Sutherland, northern Scotland. The site morphology indicates that the fen has developed over a more complex subpeat topography and that the present‐day features are unrelated to the original mineral surface. Stratigraphical information together with radiocarbon dates and pollen age estimates suggest that the mire developed initially in one, perhaps two, narrow gullies as poor fen peats from the early tenth millenium BP. The mire then spread on to surrounding slopes with the onset of ombrotrophic peat accumulation, where the most recent basal age estimate is ca. 3500 yr BP. Poor fen peats extending to the surface began growth at ca. 2850 yr BP, once this ombrotrophic peat cover was complete. A reconstruction of mire conditions based on macrofossil, pollen and other microfossils shows the nature and timing of these changes in more detail. The findings show that the existing models of patterned fen development are not applicable to the Scottish systems. Instead, the poor fen systems are recent developments, which may overlie extensive earlier peat deposits of ombrotrophic character, and are unrelated to earlier peat development. The site has probably developed as a result of localised hydrological changes within the underlying peat body and mineral base, resulting in increased volume and quality of the water supply. It is suggested that this may be by the development and emergence of sub‐peat pipes at the head of a suitable slope. Copyright © 1994 John Wiley & Sons, Ltd
Abstract.
1993
Aravena R, Warner BG, Charman DJ, Belyea LR, Mathur SP, Dinel H (1993). Carbon isotopic composition of deep carbon gases in an ombrogenous peatland, northwestern Ontario, Canada.
Radiocarbon,
35(2), 271-276.
Abstract:
Carbon isotopic composition of deep carbon gases in an ombrogenous peatland, northwestern Ontario, Canada
Radiocarbon dating and carbon isotope analyses of deep peat and gases in a small ombrogenous peatland in northwestern Ontario reveals the presence of old gases at depth that are 1000-2000 yr younger than the enclosing peat. We suggest that the most likely explanation to account for this age discrepancy is the downward movement by advection of younger dissolved organic carbon for use by fermentation and methanogens bacteria. This study identifies a potentially large supply of old carbon gases in peatlands that should be considered in global carbon models of the terrestrial biosphere. -Authors
Abstract.
Charman DJ (1993). Patterned fens in Scotland: evidence from vegetation and water chemistry.
Journal of Vegetation Science,
4(4), 543-552.
Abstract:
Patterned fens in Scotland: evidence from vegetation and water chemistry
Mires with attributes similar to the patterned fens of boreal continental regions have recently been reported from northern Scotland. This paper reports on the vegetation and water chemistry of 18 of these sites. Most of the 18 mires displayed remarkable uniformity in their vegetation, with Carex lasiocarpa being a main character species. Major variation of plant communities is associated with microtopographical niches, similar to those found on ombrotrophic mire systems and secondarily with pH and conductivity of surface waters. Nine vegetation noda are described and compared with existing phytosociological associations and National Vegetation Classification (NVC) communities. The dominant Sphagnum ‐ Carex communities are intermediate between the Oxycocco‐Sphagnetea and the Caricion lasiocarpae and are thus difficult to assign to existing associations or to NVC communities. Although there is a large variation in pH of surface waters (3.9–6.6), mean measurements for terrestrial and aquatic communities are 5.12 and 5.51 respectively. pH levels are comparable with poor fen systems elsewhere in Britain and slightly higher than patterned fens in continental regions of Europe and North America. The vegeta‐tional and chemical attributes of these sites therefore confirm the existence of true patterned fen systems in the British Isles. 1993 IAVS ‐ the International Association of Vegetation Science
Abstract.
1992
CHARMAN DJ (1992). Blanket mire formation at the Cross Lochs, Sutherland, northern Scotland.
Boreas,
21(1), 53-72.
Abstract:
Blanket mire formation at the Cross Lochs, Sutherland, northern Scotland
A brief review of the genesis of blanket peats is presented, together with detailed analyses of basal peats from northern Scotland. Particular attention is paid to local factors affecting peat growth and the problems of sampling and interpretation arising from them. Macrofossil and loss‐on‐ignition analyses of four peat‐mineral interfaces solve many of the terminological problems of such profiles and indicate that interpretations based on field stratigraphy alone are uncertain. Pollen analyses of two profiles from contrasting microtopographic situations show well‐defined vegetational change associated with early peat development. Fully organic ombrotrophic peat is present from 6805 ± 50 BP at one site, following anthropogenic burning from c. 7500 BP and partial recovery of the open birch woodland. A change from birch woodland to Calluna heath occurs at approximately the same time on a more freely drained site with much later peat development, following further burning from 4890 ± 65 BP. Anthropogenic activity is clearly associated with changes in soil and vegetation preceding peat formation, and the role of climatic factors remains equivocal. Copyright © 1992, Wiley Blackwell. All rights reserved
Abstract.
Charman DJ, Warner BG (1992). Relationship between testate amoebae (Protozoa: Rhizopoda) and microenvironmental parameters on a forested peatland in northeastern Ontario.
Canadian Journal of Zoology,
70(12), 2474-2482.
Abstract:
Relationship between testate amoebae (Protozoa: Rhizopoda) and microenvironmental parameters on a forested peatland in northeastern Ontario
The relative abundance of species of testate amoebae (Testacea; Rhizopoda) was established from 107 surface moss samples from a forested peatland in northeastern Ontario. These were related by multivariate analysis to a number of microenvironmental conditions including soil moisture content, water table, bulk density, humification, dominant peat component, pH, peat depth, depth o.f living moss, dominant surface moss species, vegetation type, microtopographical position, and artificial drainage. Moisture conditions play a key role in determining the species assemblages, pH being a secondary factor. Other environmental parameters related to species assemblages do not necessarily indicate a direct ecological link but are also associated with moisture and nutrient conditions. Individual species are ranked in terms of their preferred moisture conditions and compared with data from Finland. Certain species are restricted to either dry or wet conditions while others tolerate a wide range of moisture. Calculating weighted averages of substrate moisture contents for a greater range of species sampled from a larger number of sites will allow the development of transfer functions for constructing palaeomoisture curves from peatlands.
Abstract.
Charman DJ (1992). The effects of acetylation on fossil Pinus pollen and Sphagnum spores discovered during routine pollen analysis.
Review of Palaeobotany and Palynology,
72(1-2), 159-164.
Abstract:
The effects of acetylation on fossil Pinus pollen and Sphagnum spores discovered during routine pollen analysis
Supposedly "standard" procedures for pollen analysis vary in terms of precise treatments used. Acetylation (often incorrectly called "acetolysis") is in common usage to remove cellulose from samples, but the duration of the treatment is variable. The effects of the duration of acetylation on fossil Pinus pollen and Sphagnum spores are reported from a peat core in northern Scotland. Statistically significant differences in Sphagnum spore curves result from acetylation times of 1 and 10 min. Pinus pollen appears to be less severely affected. Despite 50 years of pollen analysis, fundamental research on the effects of acetylation and other chemical treatments on pollen counts is necessary. © 1992.
Abstract.
1988
Smith RS, Charman DJ (1988). The vegetation of upland mires within conifer plantations in Northumberland, northern England.
Journal of Applied Ecology,
25(2), 579-594.
Abstract:
The vegetation of upland mires within conifer plantations in Northumberland, northern England
Afforestation in Northumberland since 1920 has resulted in extensive areas of conifer plantation at Kielder in the NW of the county. Upland blanket mires too wet to afforest were left unplanted. These now exist as islands of open land within conifer plantations. The wildlife conservation interest of a number of these island sites is considerable because of the undisturbed natural state of the Sphagnum communities. The vegetation of these sites is classified by numerical methods into ombrogenous mire and non-mire moorland types. Cover of ombrogenous mire, wet heath and "dry' moorland species were related to a site's edge-area ratio, and the length of time that a site had been surrounded by forest. There were more ombrogenous mire species and fewer dry moorland species at sites which had a relatively short boundary with the forest and when only a short time period had elapsed since the surrounding forest was planted. from Authors
Abstract.
